Castle Swimmer: Volume 3 [A Graphic Novel]

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, Fantasy, LGBT, Comics, Romance, Queer, 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.

[✨sofia✨ · Rating 5 out of 5]

I love them I love them I love them

[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!

[Kassu · Rating 3.75 out of 5]

4-⭐

This series has been cute and fun. But Kappa and Siren were separated in the last volume, so... get ready for: no romantic progress!

OK, I don't really fault this volume for having separate storylines for our main characters. While we are all probably reading this for the cute romance, and I sort of hate how long-winded serials can get (I have special side-eye for web comics), there is a need for these characters to grow separately too, and not just be cute and mushy together.

Kappa is trying to learn to be more selfish and Siren is finding courage to search for another way to break the curse. There is a hint of a possible bigger threat in the future. The bright spot of this volume is the silliest, cutest, little Arp - who is an axolotl or something? Super adorable. Arpdorable?

I have read the two earlier volumes as physical copies. The art has been consistently pretty, but it seemed a bit dark to my eyes. A reading lamp was not enough light to distinguish the details, everything was so dark blue. It is the bottom of the ocean, so I get it, but still. I thought digital copy might be better as one can adjust screen brightness, but I'm not sure. It was defnitely easier to perceive the images at a glance this time - reading a digital ARC - though I still would prefer more contrast. (And I don't know if there's any changes on the physical copy compared to earlier volumes.)

I received an ARC, my thanks to NetGalley, Ten Speed Press and the author/artist.


Finally, a little tirade about the different reading formats and availability, feel free to skip this:

It has taken me over half a year to read this cute little comic book. Why? Because I wasn't able to download it to my e-reader or even to iPad. Now as the archive deadline is approaching, I finally sat down to read this on my damn desktop computer screen. AGH. It is painful. Earlier this year I actually went and edited another ARC copy that had a lot of line break errors. So I could read it smoothly on my e-reader. I love my e-reader. Let me read my books on my e-reader. 😩

[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.

[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.

[Anniek · Rating 4 out of 5]

It was so fun to continue this comic series! Volume 3 has quite the change in setting, which added a lot of fun new situations. I especially loved seeing all the quirky new characters that our main characters get to meet.

Since Castle Swimmer is a long series, it's understandable that there's transitional storylines at times. Volume 3 felt a little less enjoyable because of that, since it felt more like a way to get from volume 2 to volume 4. Adding the fact that Kappa and Siren are apart during this volume, I did enjoy this slightly less than the previous volumes, because their dynamic is what makes the series so fun for me.

I will happily look forward to volume 4, because I feel like things will most likely pick up again from there.

[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

[Jamie · Rating 3 out of 5]

Cute but I think the stakes are just too low for me to continue. I need a little more drama and angst than this is giving.

[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!

[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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[Elise · Rating 5 out of 5]

Volume 3 of Castle Swimmer focuses more on Kappa and Siren’s separate journeys. Siren is determined to find a solution to the sharks’ curse, and Kappa is trying to figure out who he is aside from being the Beacon. Even though I missed having Siren and Kappa together, it was good to see their characters grow individually. They both meet new characters who will have a lasting impact on their journey going forward. I am really looking forward to their reunion.

I also really enjoyed the mini bonus episodes and concept art at the end!

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

[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.

[Grace · Rating 4 out of 5]

Really love that we've moved away from what was happening in the last 2 volumes. There's so much character and plot and world growth in this one.
Kappa and the witches storyline is my favourite so far, the witches are so funny.

I am a little confused by Kappa's fin colour tho. On the cover here it's yellow. But on the Webtoon App where I read it Kappa's fins turn red for some reason after the events of volume 2. Maybe that's just on Webtoon and in the physical copy it's still yellow? Idk, it's never explained either.

[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

[sani · Rating 5 out of 5]

I was so excited when I received the ARC for the next installment in the Castle Swimmer, I used to read this story on webtoon and I loved it. Being able to read it again, this time as a published book warms my heart. This story and its characters are so charming and hopeful that readers will feel at home from the first chapter. I LOVED the mini episodes at the end as well as the concept sketches of the witches from this volume.

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

[nico · Rating 5 out of 5]

my babies 🙁💘

[suonnahbooks · Rating 3 out of 5]

3.5⭐️🥰

[gray (my.rainbow.bookshelf) · Rating 4 out of 5]

Webtoon is actually so dangerous sometimes bc I am flying through this series

[Aubree Lanman · Rating 4 out of 5]

Such a delight, per usual 🙂‍↕️ This installment gave me She-ra vibes and I am so here for that. 👏🏼

[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.

[Terri · Rating 4 out of 5]

3.5 stars RTC

[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.

[Mila · Rating 4 out of 5]

Every single time I pick up a volume of this series, a smile automatically appears on my lips. And every time I spend the entire time I'm reading, grinning til my ears. It is always a pleasure to find Kappa and Siren again and to join them in the pursuit of their adventures.

In this volume, the story continues to get gradually darker and even more intriguing, making us shake with excitement at what is coming. I adore the direction that the plot is taking, and I feel like it's a shared feeling. Martin truly is dealing with her plot in a beautiful way! But if this gets darker - mostly on Siren's side, our boys are separated in this one volume! - It also benefits from some humour brought to us by some new characters - the evil witches, whom I have found to be very interesting characters as well as nicely written ones - and some known ones - Arp was excellent in this one, but I might be biased by how adorable they look.

The art is still just as good and colorful while the story allows us to explore new areas from the ocean that we hadn't seen before. And that also brings us some nice changes in our favourite characters' design, which is always something that we like to see! Siren and Kappa are such adorable and well-written characters, and while I grieve a bit that we don't get to see them cross paths in this one - in the next one, folks! - it was truly interesting to see them go their own way.

This marks a third volume just as great as the first two, and that leaves us wanting more - if it were up to me, I would probably binge the entire series in one sitting - while making us delighted by its existence. I would also like to thank Netgalley and Ten Speed Graphic for sending me an e-ARc of this one. This excellent volume releases on March 17th, and I can only encourage you to grab a copy - or a copy of the first volume if you haven't done that already - because it is really just that good and fun!

[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?