Castle Swimmer: Volume 3

Castle Swimmer #3

by Wendy Martin

Kappa and Siren’s adventurous journey into the vast ocean begins in this exciting third installment of the hit Webtoon series Castle Swimmer.

After leaving Siren to recover from his wounds in the shark castle, Kappa finds himself out in the big wide ocean once more. Minutes into his newfound freedom, another prophecy intervenes, pulling him towards a giant demigod crab scuttling along the ocean floor. As Kappa tries to figure out why he is drawn towards this crab, he comes across three magic-wielding octopi with tragic pasts and uncovers more about his greater purpose as the Beacon.

When Siren finally leaves the shark castle a month later, Kappa is long gone. Alone in the greater ocean that he’s only ever heard about, Siren quickly finds that he’s unequipped to fend for himself. After having his supplies stolen by thieves, Siren finds himself by luck in the company of a young fish and his mother and joins them on their travels. As they teach him to fight and tough it out in the wild, Siren begins searching for a cure to his curse.

This beautiful graphic novel collects episodes 42-65 of Webtoon’s Castle Swimmer and includes three new mini-episodes plus exclusive bonus content.

Genres: Graphic Novels, LGBT, Fantasy, Comics, Queer, Romance, Young Adult

288 pages, Paperback

Published March 17, 2026

Reviews

[Brooke · Rating 4 out of 5]

⭐️ 4 stars ⭐️

Another fun installment full of adventure and creatures and new characters.
I love the art style of this comic and the pretty ocean world, but hope the next one brings more action and more of Kappa and Siren together. I need more cuteness!

I received a free copy of this book from NetGalley, and am leaving this honest review voluntarily.

[rayhanah · Rating 3 out of 5]

3.5 ⭐️
adore this series so much everyone should read it!! 🥹

[Manon (bookswithonno) · Rating 3 out of 5]

*3.5 sterren

In dit deel gaan de personages allebei los op avontuur en ik vond dat toch wel minder leuk. Ook ben ik benieuwd waar het verhaal nu precies heengaat. Wel vond ik de grapjes weer erg leuk, de art weer fantastisch en de personages allemaal heel leuk. Ik blijf zeker weten doorlezen🥰

Bedankt NetGalley voor de e-arc van volume 3🫶🏼

[Emily · Rating 5 out of 5]

Thank you to netgalley and Ten Speed Graphic for providing an eCopy of this comic!

I really enjoyed this volume a lot! I complained a lot about the humor in my volume 2 review, but I didn't feel that way at all while reading this volume. The humor didn't detract from the story at all, instead it just made some of the character interactions cuter. I also enjoyed all the new characters. The witches are fun. I'm hoping we will get a backstory for them in the next volume. I still really like both Kappa and Siren. Siren mostly just kind of swims around almost dying. I figured I would be annoyed by how incompetent he was, but I honestly didn't mind, I did sometimes get some secondhand embarrassment from him though. As for Kappa, he mostly spends this volume trying to juggle his compulsion to help others with his desire to put himself first. We also get quite a bit of world building in this volume, we meet new mer-people, go to new places, and even get some creation-type lore. Plot-wise, this volume is mostly setup for the next arc and doesn't really stand well alone. Think of it more as the first third in a novel rather than a complete story in itself.
I originally read this comic on webtoon and I think we are getting pretty close to where I quit reading the first time. So I'm looking forward to reading the next volume and seeing what happens next!

[Frank Chillura (OhYouRead) · Rating 4 out of 5]

This volume of Castle Swimmer finds our favorite sparkly beacon, Kappa, befriending a group of “evil” sea witches. They’re on a mission to find a minigod, with nefarious plans, but there has to be some form of causality for it. While we do find out some information about them, when asked if they are a certain breed of creature, their response left me with even more questions. I’m really hoping that we learn much more about them.

Our favorite shark princeling, Siren, is healing from his injury, but can’t wait to be able to finally find a way to stop the curse that has been hurting his people. And if he meets back up with the sparkly one, he won’t be sad about it.

With the way the story is progressing, it definitely feels like there are many more volumes to come and I’m not mad at that.

Thank you to the publisher and NetGalley for the gifted eARC.

[ally_owos · Rating 5 out of 5]

Caught up to all the free stuff. God I’m not ready for this finale. I’m gonna be bawling my eyes out

[dobbs the dog · Rating 4 out of 5]

Received from NetGalley, thanks!

I am enjoying this series, though it is very low stakes everything. I found that this volume really dragged a lot, even if the artwork is lovely. I think I can see where it's going, but it is taking its sweet time. I saw another review say that this could be a result of it being a serialized webcomic, and I can absolutely see that being the case.

Despite this being fairly slow plot-wise, I'll keep reading!

[Emmaline Savidge · Rating 3 out of 5]

This series is just perfectly middling. I think if you enjoy something like Heartstopper but want a light fantasy element then you'd have a lot of fun with this. Now that I'm three books in I've realized that the stakes are just a bit too low for me and our leads act far too young. I also think this series is suffering from being a serialized story that was adapted. When you're just releasing a story page by page online sometimes we end up with a whole book where not much happens. It's hard as an artist to have tight story beats when on a release schedule, but I highly recommend that people go to the Ngozi school of webcomics. Check Please has a really solid discrete structure and when it was adapted into a physical book it worked really well. Castle Swimmer isn't fanfiction, but I think that Dan Olson does a really great job outlining some of the pitfalls that can come with serialized fiction like fanfic in his 50 Shades of Gray youtube video. I just get a vibe that this story is kinda puttering on unsure of how or when it will get to it's conclusion.

Thanks to the publisher for providing me with a free e-ARC in exchange for my honest review.

[Smut Report]

Heat Factor: On pause

Character Chemistry: They’ve been separated by fate!

Plot: Kappa goes on a quest(?) not to be himself anymore and joins a band of sea witches. Siren goes on a quest(!) to improve himself and almost dies several times.

Overall: This book is cute in a twee way, and I will probably keep reading by myself, but I think it’s time for the series and the blog to part ways because the burn might be too slow.

Read our full review at The Smut Report

I voluntarily read and reviewed a complimentary copy of this book. All thoughts and opinions are my own. We disclose this in accordance with 16 CFR §255.

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[Cassandra · Rating 4 out of 5]

*An ARC was provided by NetGalley and the publisher in exchange for an honest review*

This volume felt like the training arc of a shonen anime. Both Kappa and Siren go on little journeys through the ocean to find each other and end up finding new crews (Kappa falls in with a trio of sea witches more set on mischief than anything else and Siren... well, you'll see). It felt a bit dragged out compared to the past two volumes, but might be in part because every scene where Kappa and Siren are apart fills me with a visceral yearning for their reunion.

I read this series back on Webtoon back when it originally came out, so it's been a blast experiencing the series again so many years later and seeing it reach new audiences with these physical bind-up collections.

[Ryleigh · Rating 4 out of 5]

Thanks to Ten Speed Press and NetGalley for a free ARC. All opinions remain my own.

The third volume of Castle Swimmer follows the aftermath of Prince Siren's secret being revealed to the shark mer. He must die in order for the shark mer to stop being injured so often, but the queen lied and said that the Beacon had to die. With the queen in disgrace, she stepped down from the throne and a new mer of Siren's choosing is now the heir. Siren thinks his missing father has answers about the curse, so he goes out to find him accompanied by the adorable axolotl Arp. Meanwhile Kappa the aforementioned Beacon is forging his own path as well, seeking freedom from the weight of his heroic destiny.

I enjoyed this new volume. All of the new characters were a joy to meet but especially the sea witches. Even though they are of questionable morality, the scenes featuring them were hilarious. I like the effort to develop Siren and Kappa separately but I can't wait for them to get back together. Although I am a bit disappointed with the cliffhanger ending I'm still looking forward to future volumes.

[rose ✨ · Rating 3 out of 5]

“and the sea is so big! bigger than i ever dreamed!”

this was definitely a filler volume with both kappa and siren exploring and meeting new merfolk on their separate quests. i didn’t love the art here as much as in the previous volumes, something about the lines felt less detailed and thoughtful.

i received an ARC from the publisher via netgalley in exchange for an honest review.

rating: 2.75/5.0 stars

[Elise · Rating 5 out of 5]

I loved it! I will share my full review the week of publication as per the publisher’s request.

Thank you NetGalley and Clarkson Potter/Ten Speed Press for the ARC!

[nicole · Rating 5 out of 5]

my babies 🙁💘

[Anna · Rating 4 out of 5]

I'm really loving this series! I finally caved and started reading the rest on webtoon and let me tell you, it only gets better.

[Mariana · Rating 5 out of 5]

Oh I missed Kappa and Siren! This is the arc in which they go their separate ways to learn and get stronger before they find each other again. I know they’ll be together again but goddd I just them to find each other, it’s gonna be so great. I loved dipping back into this world, thank you for the early copy!

[Steff Fox · Rating 4 out of 5]

Have you ever read two books in a series that introduce a cohesive story so phenomenal the follow up, despite how good it is, feels a little off? It’s like there’s this uncertainty about what to do next, where to take the story—and maybe it’s the fact that Kappa and Siren spend the entirety of this volume apart, but Wendy Martin’s volume three of Castle Swimmer just doesn’t have the emotional connection that the first two volumes do. And I say this as someone who absolutely adores the series and has read everything available on Webtoon.

But I have to be honest when I come into this section of the story and say that it feels like following a story that has reached the big climactic end only to have the slowest of starts to the next piece of the journey. It almost feels like an epilogue that’s not an epilogue—the slice of life that leads to the next adventure because we’re just not quite there yet. And don’t get me wrong, I adore these characters so the story is still deeply entertaining and engaging and I’m eager to gather up all that I can…but there’s very little emotional buildup here outside of some small personal tidbits of our two male leads.

It’s like the filler episode to the new buildup; because we definitely get the introduction, the lead up to where everything is going, though it’s a little more pronounced with Kappa than with Siren. But we don’t get there quickly and it makes sense given the snap, poof introductions of all these new characters. I adore the characters, don’t get me wrong, but we barely get the chance to breathe before another group is thrown our way. I’m not sure exactly what I’m looking for when it comes to this next step in their journey, but it was definitely something a little more cohesive with a definitive theme. And I can’t help feeling like Martin is still trying to get her footing with the plot of her story now that she’s resolved the core conflict of volumes one and two.

I received a copy of this book from NetGalley in exchange for an honest review.

[Snarky Hatter · Rating 5 out of 5]

I am so excited to have received an ARC of volume 3 of Castle Swimmer from NetGalley. I love this series. I started reading it years ago when it was just getting started on WEBTOON. However, life happened, and part way through the series I got distracted. I was never able to finish the series, so getting an advanced copy of Volume 3 was such a treat, especially because it contains the chapters I was reading right before life distracted me.

Personal life aside, opening this book was so refreshing. Wendy is such a talented artist. Her use of color and line art are so skillful. She manages to make everything look so soft and beautiful. She does it in such a Ghibli fashion too, where there is not necessarily a lot of detail to the scene, yet there is still something so beautiful and magical about it.

She also has a bit of that Ghibli humor, and you really see it with the "Evil" witches in this volume. Especially with Mucku who not only has that humor, but moves like a Ghibli character. The way she moves her hands and arms constantly remind of Sophie from Howl's Moving Castle when she teases Markel.

And all this doesn't even get into the story. Kappa and Siren have parted ways since the last volume, and while it is bittersweet it is much needed. We've reached the part in the series where Kappa and Siren are learning and growing, and not only will that growth help them as people gain the traits and confidence that they need, but it's going to help them reconnect and grow closer to each other.

And note: this isn't me saying it as a spoiler (like I said I never finished the series), but it is very clear based off what is happening in the story that this is the intent with the current subplot.

It's such good storytelling paired with beautiful and lively art, and I'm excited to read more.

[mad mags · Rating 4 out of 5]

(Full disclosure: I received a free e-ARC for review through Edelweiss.)

After the absolutely SHOCKING events of Volume 2, Susca is out as queen of Shark Castle, with Siren's childhood friend Skiff in training to take on the role. Siren, meanwhile, is determined to find a way to break the curse on his people - and so, against the advice of the elders, he goes off on his own in search of his long-lost father. Well, not entirely alone: hidden in the bag Kappa left for him is an adorable axolotl named Arp. He might not look like much, but Arp is far fiercer than Siren, whose sheltered life definitely did not prepare him for this journey.

Meanwhile, Kappa keeps bouncing around the ocean, pulled by the prophecy to a dodgy minigod crab named Ogo. As it just so happens, a trio of "evil witches" - who may or may not be the last of the fabled Octalia - are in search of Ogo, and they enlist Kappa to help them find him. In exchange, he asks Mucku, Mono, and Queen Nethimir to teach him how to be an evil witch, too - that way he can embrace greed and live only for his own selfish desires. (If only! Kappa is too pure for this world!)

CASTLE SWIMMER continues to be one of my favorite strips - it's so warm and cozy, like a fleece blanket or a well-worn episode of SCHITT'S CREEK - and diving back in in this two thousand and twenty-sixth year of our Lord, starring a rotting Trump 2.0, has been a nice (if fleeting) relief. Kappa is just the sweetest little merman ever, and OF COURSE he left Arp as a "guard dog" for Siren. Volume 3 also introduces us to some pretty great new characters, including the witches; Herm the hermit crab; and merpeople Pim and Pagoon, who take Siren under their wings (errr, fins?). Pagoon's training lessons with Siren - while his bemused mother looks on - are so cute, as is Kappa's transformation to a gentle goth merwitch.

Martin also introduces several new mysteries, chief among them the origins of this world. Herm reveals that the minigods are just regular sea creatures who were granted special powers by fossils - fossils possibly left by humans - suggesting CASTLE SWIMMER might be more of a post-apocalyptic story than a straight up fantasy.

Also, the Octalia! What is Queen Nethimir hiding?

[destinedreading · Rating 4 out of 5]

I first started reading Castle Swimmer on Webtoon when I began high school and I’m so glad to see it’s getting the recognition it deserves with published graphic novels while I’m in university. For me, this was technically a re-read and I’m definitely loving the series just as much as I did before.

This volume builds right off of the second volume and immediately begins with both Siren and Kappa’s adventures through the ocean as they attempt to keep the promises they made to each other. I loved how much new world building we got now that the two of them weren’t confined to the shark cave. The humour in the book was great and I also loved seeing how the two of them were adapting to their new lives and how close they kept getting to each other with adventures that paralleled to the other’s.

The new characters they both meet are all fun and have their own unique and distinctive personalities that make me excited to get to know them more. The author also did a great job adding enough to make it feel like a new phase of the overall story without overwhelming the reader. The previous characters have also all developed and grown in wonderful ways. I especially loved seeing Skiff’s training with Susca as well as Kappa discussing more of his beacon related feelings.

This series is a great one with this volume building on what we’ve seen previously in a way that’ll get you excited for more. Time for me to get the Webtoon loaded back up until the next volume is published!

E-arc provided by NetGalley!

[Lexa Riffe · Rating 4 out of 5]

Castle Swimmer Volume 3 Collects episodes 42-65 of webtoons castle swimmer.

Although Kapp and Siren have gone separate ways for now. They are both working on keeping their promises to each other. Siren is going on a journey to find his Father in hopes he can help break the curse. Kappa has met up with a group of unlikely friends that will help teach him that he does not need to make every one happy and that he can say no.

Both of the boys are taking journeys that are changing their lives in more than the ways they started the journey for. They keep each other close in their hearts, hoping that one day they will be together again.

As always this story is heartwarming and will keep you giggling. Wendy Martin has a wonderful way of hitting hard topics in a way that you can connect with and relate to, while maybe learning a lesson yourself.

The art remains beautiful. Kappa's scales are red in this volume, When i looked into it because i thought i missed something, I read it was an art choice to show he's in a new area and well he looks good in red. I do agree.

I'm loving the pacing of the story and how we get the cute fluffy moments , however those moments do truly add to the story. We end this story learning that there may be something big, and possibly scarry on the horizon for our Beacon. Will he be ready ? I cant wait to find out in volume 4.

Thank you NetGalley and Clarkson Potter/Ten Speed Press | Ten Speed Graphic for the Digital ARC.

[ivanareadsalot · Rating 5 out of 5]

I would like to thank NetGalley and Ten Speed Graphic for the opportunity to read and review this ARC.

✨Castle Swimmer: Volume 3 collects Episodes collects episodes 42-65 of Webtoon’s Castle Swimmer and includes three new mini-episodes plus exclusive bonus content.✨

🪸🪼🦈🦀🐙This webtoon is the most adorable thing I've read all year, and it just keeps getting better and better! Vol. 3's artwork was vibrant and stunning, as usual. The flow and the energy made this volume another compulsive read, and I straight up LOVED every. single. character. in this installment! Besides Kappa and Siren, who I fall more and more in love with as the story goes along, this volume had a rich cast that added layers of dynamism, humour and fun to the mix! They were some of the most engaging and expressive sugar dumplings I've read to date…but fishy…and I enjoyed the moments of sweet pining, and the funny bits that made me laugh and just how charming this whole vibe was overall! We love a costume change, and Red Kappa served ruby sparkles and a Capelet like a boss! He was all of us imagining how it would be to rock up to bae in his new look🐚🐟

🦪🐠I'm excited for more adventures with Kappa and Siren, who are making their time exploring a new way of life very entertaining, and I can't wait to see what all their gained experience and valuable skills amount to when Volume 4 comes out! LOVED THIS!🪸🪼🐋🦑

[Kat · Rating 4 out of 5]

Thank you to the publisher for sending me an eARC via Netgalley. This does not influence my opinion.

Okay, this third volume of Castle Swimmer is my favorite so far.
We see our main characters grow, as we always do, but this time apart from each other. And honestly, I think it’s good for them? They have their own ambitions and drives to pursue instead of constantly trying to save each other and kind of sacrifice themselves in the process.
Their personalities still stay very distinct and I adore how both of them keep winning people over by being themselves.
But what made this volume stand out to me were the “evil” witches and how they made me laugh out loud so many times. I love them and can’t wait to read more about them in the next volume.
The art style was beautiful, as always. I also liked how the color scheme kind of changed. At first, I thought it was about Kappa growing up and into himself, deciding to pursue his own freedom, but the author said in the notes at the back that it’s at least partially about the location. I still think Kappa should have at least reflected on that change in his scale color though, so readers wouldn’t be confused.

All in all, I really like this volume of Castle Swimmer and can’t wait for the next one.

[Katharine · Rating 5 out of 5]

This volume picks up right where the second volume left off. Kappa is back to wandering the ocean and meets three "evil witches". He ends up being "kidnapped" and roped into their journey of finding a wandering minigod. Meanwhile, Siren sets out on a journey himself. Siren says he's searching for a way to break the curse on the castle's citizens, but likely also hopes to find Kappa on the way. This volume does expand a little on Siren's new stance on his relationship with his mom and the rest of the shark kingdom's citizens. Kappa, while journeying with the octopi witches, slowly learns that maybe he can be something beyond being the Beacon. The art style was excellent as always, but the mini comics at the end that are in the new style are always a jumpscare. The new style is such a dramatic change; it never fails to throw me off.

Thank you to NetGalley and the publishers for an advanced copy in exchange for my honest review!

[Carrie Griffin · Rating 4 out of 5]

Castle Swimmer: Volume 3 picks up directly where the second volume ended with Siren out in search of his father and Kappa trying to change the way he interacts with others. The volume follows them both on different paths and is quite a bit slower than the other two before it, which I liked a lot. Gives us a chance to get to know these characters more.

The artstyle is as beautiful as ever. I liked the new design for Kappa and loved the little axolotl companion. It was so cute!

I enjoyed seeing both Kappa and Siren interacting with different characters this time around. The octupi witches were a great addition to the story. They are some of my favorite characters so far. Hopefully, we'll get to see more of Kappa and Siren together soon, but I would like to see more of their adventures with the new characters.

*Thank you to NetGalley, the publisher, and Wendy Martin for my ARC of this book. All opinions are my own.*

[rin · Rating 4 out of 5]

4.25 stars.

Thank you so much to NetGalley and Clarkson Potter/Ten Speed Press for the ARC, I absolutely loved this.

The art was stunning as always, all of the characters were so easy to love as always, I want to hug both Kappa and Siren so badly as always, and oh my gosh this was SO funny AS ALWAYS. I actually looked up axolotls for the first time ever because of Arp and now I so badly want a plushie of one. There's one aspect about the romance that I don't want to spoil that kept this from being a 4.5 for me, but at the same time I understand the decision for Kappa and Siren's storyline and as a writer myself I really respect it. I just love seeing them together so much ( ˶˘ ³˘)♡

This was fantastic, I'm so glad I got to read it, and I have no idea how I'm going to last until the next one ( ˘͈ ᵕ ˘͈♡)

[Raaven💖 · Rating 4 out of 5]

Thank you to NetGalley and the publishers for this ARC in exchange for my honest review!!

I didn’t really remember this story well until I started reading. But this is a fun series! I love Kappa’s slutty little witch outfit. There’s so much that needs to be explained and explored and I’m glad that Siren was able to make the journey to find his Dad. And I hope he and Kappa reunite because they are adorable. And honestly all the sharks are!! The whole village is so cute! And they love Siren so much. And even when someone screws up really bad they are forgiven and life goes on. It’s such a wholesome place. I can’t remember why the guy with no eyes has to stay in that cave but he’s really cool. The evil witches were so funny too. Like I was cracking up at them. And the mystery revolving around the minigod the witches are looking for is super interesting.

[Lucy Kirby · Rating 3 out of 5]

Castle Swimmer picks up where volume 2 left off. Siren decides to leave the cave and search for his father after his mom's betrayal. We get to see some glimpses of what happens to the sharks while he's gone too. Kappa is off still being dragged around to different prophecies, but this time he's attached to a demigod who keeps disappearing. He meets a group of witches who are also looking for someone. I enjoyed the new side characters introduced in this volume, but it was the weakest so far due to the structure of the story. It was sad only getting to see Siren and Kappa together in flashbacks, but at least we had those. The art continues to be adorable. Thanks to NetGalley and Ten Speed Graphic for the ARC in exchange for my honest review.

[Jordan Tu'ulauulu · Rating 4 out of 5]

Thank you to Netgalley and Ten Speed Press for an ARC!

Great installment to the series! This was the funniest volume, I love the addition of the sea witches and Kappa's journey with them. In Volume 3, Kappa and Siren are still separated but are both out in the ocean trying to find their purpose (Siren to break his peoples curse and find his father; Kappa to learn more about his role as the Beacon but also discover who he is without that title). Amazing artwork, as usual! I hope we start to see some resolution to the plot in the next volume because I'm ready for some answers! I have theories, and I know I can go look at the webtoon and find out, but I like to torture teach myself patience.

[Rhys · Rating 4 out of 5]

*Thank you to NetGalley and the publisher for a copy*

Castle Swimmer is one of my favourite graphic novel series, and volume 3 might be my favourite so far! I love Kappa and Siren, and I’m so excited to see how their story continues.

This volume focuses on Siren going outside of the cave to try and find Kappa. Kappa, on the other hand, is now helping a trio of witches to find a minigod.

The adventures both of them go on is so fun. I loved the backgrounds in particular, it’s so vibrant and pretty!

4 stars. These are such enjoyable graphic novels and I really need to know what happens next, lol!!

Highly recommend this series if queer mer people interest you!