As usual, my review will cover the entire series from start to end (all 12 volumes). I'll be talking rather extensively about several parts of the manga, so there will probably be a few spoilers about a few specific things, mostly regarding the relationship of Fumino and Kazuma.
I've reread this manga several times since I was a teenager and while I do have a general fondness for the tone, art, characters, plots, comedy, and what not, since it has a lovely art style and a very sweet tone, I'm an adult now and have developed a greater awareness of the world that has made me realize that a core principle of this book is severely flawed:
A teacher should not date/marry/be romantic/be sexual with a student and a 24 year old person should not date/marry/be romantic/be sexual with a 16 year old person.
What's even more, a 24 year old person should not want to be with a 16 year old and they should not wait in the background for them to hit age 18 before initiating a more intimate physical relationship, as that's literally a quality of sexual grooming and a tactic predators use to avoid legal trouble.
Had this not been an issue, I'd probably give this manga a 4 or 5, but as it stands, I can only in good conscience give a 2.5, MAYBE a 3, and I do hold a major criticism about it despite my higher rating and fondness.
Now, before anyone raises a hand to say something against my criticism of why student-teacher and teenager-adult relationships are NOT okay: I am fully aware that Japanese law tends to have a very low age of consent and that, in the context of Japanese law, a 16 year old being with a 24 year old may not be illegal or even that socially taboo.
However, legality does not equate to meaning that something is ethical. While the two often align side by side and we hope that our laws reflect ethics, they are not mutually exclusive concepts.
I also know for a fact that Japanese law saying "13 is the age of consent" is a gross oversimplification of actual Japanese law and isn't the whole picture. It's also really only ever used by creepy, predatory people who want to justify why they think having sex with 13 year old Japanese children is totally fine.
Firstly, there's actually a law released after the "13 is age of consent" law that affects this definition and forces it to include girls up to age 16 under the definition of "minor" (the law was part of a child welfare act, by the way), only exempting them in a circumstance where they're married (something that must be done with parental consent, as discussed below).
Secondly, most prefectures have many "corruption of minors" laws in place that add additional protections on top of increasing the age of consent. For example, in Tokyo, the age of consent is age 18 and marriage cannot be legally done without parental consent until age 20. If people want to marry sooner, it's with parental consent and women must be 16+ and men must be 18+. There are also instances where relationships with age gaps of any degree require parental approval to prove "sincere romantic relations" as a clause to be exempt from laws seeking to protect minors from abuse by adults.
Thirdly, although there's an uncomfortable amount of people who are okay with things of a pedophilic, predatory nature in Japan, as a whole, Japanese society recognizes the age of 20 as the age at which a person is truly an adult, celebrated with a national holiday. So, it's not as if Japanese society isn't aware, it just has some terrible laws.
Fourthly, there's currently a huge social movement within Japan to undo the "13 is age of consent" law and make it nationally much higher, in the 16-20 year old range, so the law may change any day now.
As of 2023, the age of consent is now 16 across the whole country. Due to the hard work of many activists and voters, the age was raised, and continues to be 17+ in many prefectures due to additional laws that protect minors. This cements my point that the law being so low did not represent the sentiments of Japanese society as a whole. Many people are still pushing for additional reforms to raise it to 18 and do more work to better protect Japanese minors and women from abuse and assault.
Additionally, there's no social or biological reasoning that teenagers in Japan would inherently be more mature than teenagers anywhere else in the world, and therefore are capable of dating adults without issue. This isn't a debate of "you can't judge a culture based on your own culture's standards." (I have seen some people use this argument to dispel concerns about minors in relationships with adults). Literally all human brains take about 20 solid years to fully develop. A 16 year old in Japan being groomed by a 25 year old is just as much of a victim as an American teen going through the same thing. Please don't try to deny Japanese children the right to be children so that you can feel okay about adults having sex with them.
We on the same page now? Good. Let's continue.
This manga kind of takes advantage of the fact that Fumino lacks parents to decide if her relationship with Kazuma is okay and if she, at 16, can marry. It kind of glosses it over and starts to regard Fumino like an emancipated minor who can decide for herself if she wants to marry, though, it seems kind of counterproductive to allow a girl the ability to marry someone and then once she's married take away that status until she's of age to put her under her husband's mercy.
Also, we'll later talk about the legality of their "marriage."
I'm not sure what Japanese law says about the legality of relationships involving someone with authority being with a person under their authority (ex: student and teacher, boss and employee, doctor and patient, lawyer and client, etc.) but the nature of such a relationship is a contributing factor to the issues with Kazuma and Fumino being together.
Since this series wants so heavily for Fumino and Kazuma to keep their relationship a secret, I believe that there probably is some illegality to it and also some degree of social stigma, enough that the school where Fumino attends and Kazuma works would likely punish one or both of them, if indeed their relationship was made known to the faculty (Kazuma would likely be fired and Fumino could be expelled).
I will say that Kazuma is not The Worst possible outcome this manga could have had for a male lead and, as far as older male leads goes, he's rather harmless. He doesn't really touch Fumino (hence the title "Faster than a Kiss"--they're married without ever having even kissed) and he does keep a certain distance from her physically and emotionally, even encouraging her to find love with someone her own age and being adult enough to recognize that it's likely her feelings for him are just a crush and that she'll eventually outgrow them, which makes him hesitate in encouraging/reciprocating (but only at first).
Sadly, because the naive teenager says "Uhm, no, my feelings are legit and you have to be responsible for me forever" we're supposed to dismiss him being an adult who has reasonable qualms with their relationship and go "Yes, true love triumphs over all!"
Like, we were so close with Kazuma, but the author wanted to be like "no, no, don't agree with him, he's wrong, their relationship is good, you should want it."
The moments where Kazuma reveals feelings of a romantic nature and does things that speak to him being romantically attracted to Fumino (such as showing jealousy, kissing her neck, hugging h telling her he wishes to possess her, alluding to his attraction to her, etc.) are reserved for specific moments within the narrative, usually relating to Fumino realizing how she's grown feelings for Kazuma and her attempting to further their relationship as a result.
Kazuma's actions generally amount to him admitting his own feelings and some chaste physical contact, and their relationship usually goes back to being light and carefree after this emotional moment, but, still, just because he didn't grope her or have sex with her doesn't mean it's okay to act like that towards a 16 year old.
When I read about this man who operates under the pretext of being this girl's husband and says things like "I want to bind you as a man, too" and "if we continue, I won't be able to stop" and behaves in any sort of romantic way towards her, even if he doesn't cross certain lines, I can't help but think it's like... he's having his cake and eating it, too.
Because not only does he have an extraordinary amount of control over her life as both her husband and teacher--which allows him to cultivate her affection/trust for him while stamping out the competition, like his own appropriately aged brother, and making it so he cannot be untangled from her daily life, which would allow her clarity to analyze their relationship and her feelings--it provides him access to her emotionally and physically in a close relationship that clearly comes with a romantic/sexual connotation while he waits for her to become old enough for a more intimate degree of physical contact.
Which, again, this kind of stuff is considered grooming.
Sure, he ultimately doesn't hurt Fumino or make it seem like he wouldn't let her go or be with someone else if she wanted to, but it's a weird and bad situation because she's clearly at his mercy as someone younger who looks up to him and is enamored with him. She isn't in a position to be immune to any manipulation or really have the wherewithal to recognize it.
The reasons why age-gaps and power-imbalance relationships are inherently bad is because when two people don't stand on equal footing, even if the person with power doesn't overstep and abuse their power, the person who is under the other's power will always be subject to that possibility and is therefore going to alter their behaviors to be subservient to the other's will.
If a person is in a relationship where dissent can be punished in a major way or they're emotionally powerless to the other, it becomes murky as to whether or not the person is acting of their own free will or just deferring to the will of their partner to avoid negative consequences in their life and relationship.
Kazuma is both Fumino's husband* (I'll speak on this later, as I said, their marriage isn't straightforward) and her teacher, so he's in a position that allows him to basically control every aspect Fumino's life, which leaves Fumino with little agency or power over to advocate for herself. At home, at school, Kazuma has the power and authority, plus, he has power and authority over her little brother, which is also a means by which he could manipulate Fumino.
It's not necessarily what he does so much as what the power and authority imbalance ALLOWS him to do.
Fumino is someone who is less experienced, less powerful, and less able to process things and make good choices because, at the age of 16, her brain is still growing and she is still in the processing of becoming independent.
The relationship is simply inherently skewed in an unhealthy way by nature of Fumino, the minor, being wholly dependent on Kazuma, the adult.
He doesn't have to manipulate her malicious or sexually abuse her for her to be in a situation that is precarious, since he has power over her and she isn't in a position to see abuse of that power if it occurs, and that alone is problematic.
It's why most places have laws in place to try to prevent this; the power imbalance inherently allows for exploitation and it can be difficult to decide whether the relationship is indeed healthy or if the alleged victim is merely being manipulated or threatened into behaving like it is.
The two of them end up "married" because Kazuma wants to see Fumino taken care of after she and her brother run away from a relative's home; he is, in fact, the only adult who looks for them and seems to care about their well-being. We later find out that the marriage wasn't actually legally binding, since Kazuma never submitted the marriage paperwork, and that the marriage ultimately was the only way Kazuma saw as a way to make his situation with Fumino work, not only because she was resistant to his help, claiming that he wouldn't care enough to take full responsibility by marrying her, but because as an unrelated adult, he didn't really have the grounds to take responsibility for Fumino's well being in any other context besides becoming her husband.
Despite this fact, however, Fumino believed it was legitimate and acted accordingly, and Kazuma allowed himself to show interest in her and let her believe this facade, so we'll continue on that premise.
Now, the legality of everything in this series isn't really well implemented (clearly.)
Despite Fumino and her very young brother fleeing their relatives' care and having no parents, no one from the courts or police ever come sniffing after things to verify that the minor has a guardian and that the guardian is taking care of their charge.
Fumino transitions from being under her relatives' guardianship to Kazuma's without incident. Did her relatives not report her missing? How did Kazuma know she had run away then? Why didn't the relatives, if they didn't want Fumino anymore, forfeit custody so the courts could find a new guardian? Why were her and her very young brother's welfare never checked into by authorities? Even if Fumino, at 16, isn't a priority for the system since she's so close to aging out, her brother, who is only in preschool, should be.
Since Kazuma can't actually be her legal guardian, since their relationship is a secret and he never submitted their marriage papers to be processed as a legal document, does the school and court just... presume Fumino is still with the relatives she ran from, despite them never appearing to do anything that a legal guardian has to for kids this young? Teppei especially should have flagged the system on multiple accounts because his 16 year old sister can't act in place of a guardian as a minor herself.
I guess that's why Ryo exists; he babysits when the couple needs alone time and then can lie on school records to keep Fumino and Teppei's lack of legal guardianship a secret so they can remain with Kazuma. How wonderful and illegal!
Usually a child who loses their parents is assigned by the courts to a new situation; despite Fumino being a teenager, until she's an adult, she should be legally obligated to exist under the guardianship of someone and that person be held accountable for her whereabouts and well-being.
The book does later attempt to have Fumino's paternal uncle become their guardian and she refuses and goes to be with Kazuma but like... her uncle should have gone to the courts and been like: "Okay, I want proof of my niece's marriage and I want to contest it because, as a 16 year old, she needed the consent of a guardian, which I doubt was granted to her." and there would've been a whole thing about it, but because this story didn't really examine things outside of "wouldn't it be fun if a teacher and student married and had to keep it secret?" none of the legality of this situation is really ever addressed outside of it being a minor conflict for them as needed.
Anyway, outside of this glaring criticism, which is so big because it's so central to the series, I do have some fondness for the series.
I just REALLY wish it aligned more with my ethics because despite this not being the worst, I still very much dislike student and teacher romantic relationships that involve high school students and generally think of them as precarious, bad things that aren't worth the risk.
I don't want to just go "well, it could have been worse" because I don't want any part of this normalized or not treated with the severity that it should. Just date people your own age who you don't have the ability to control/ruin the life of. That fixes and avoids SO many issues and is just so much easier for everyone.