‘Marriage Toxin’ Is Bringing Romance to Shonen in a Big Way

Last year, Dan Da Dan was a breath of fresh air in the anime scene, putting romance front and center in its hodgepodge pastiche of sci-fi yokai action. But it, like many other shows of its ilk, comes with the caveat that its perspective on love is only that of teenage angst, not the more profound twinge of an adult romance. Thankfully, Marriage Toxin has been the cure for what ails manga readers who want a little love in their battle shonen, and it’s got an anime adaptation coming later this year.

Marriage Toxin, written by Joumyaku with art by Mizuki Yoda, follows a hitman named Hikaru Gero who comes from one of the five big clans of assassins. All of whom, naturally, have supernatural abilities. His power, however, is as a poison master. While he’s skilled at completing contract killings, he’s a cherry boy when it comes to anything romantic. Gero was resigned to never marrying until his family forced his younger queer sister to continue the family line herself. Now, with the help of Mei Kinosaki, a cross-dressing marriage “swindler,†Gero puts an earnest foot forward to learn all the dos and don’ts of talking to the fairer sex and building a romance worth fighting for in pursuit of his future wife.

Rather than treating the series like your garden-variety harem slop, Marriage Toxin avoids those tropey shortcuts by treating its premise with real heart and humor. In so doing, Marriage Toxin lines up a whole spectrum of eligible bachelorettes from the demure, timid, headstrong, and clumsy, each carrying their own mix of insecurities and strengths, and the manga unpacks in its dates/missions so there’s always someone for readers to latch on to as their bias.

But aside from the obvious shipping, the real anchor for the series is Gero himself. His gentlemanly, chivalrous, and soft-spoken sincerity turns every meet-cute into a romance worth investing in as he searches for his life partner.

All of this unfolds alongside shonen-style battles reminiscent of Sakamoto Days—big set pieces, inventive power sets, and comedic timing. There’s dead ass an assassin whose power is video game logic where he uses debuffs on others and especially himself, and that’s not even the raddest fight in the series. While Gero is admittedly not especially strong, relying instead on poison‑master cunning and digging in deep like all shonen greats are wont to do, his unflinching determination to ensure none of his potential partners end up stripped of agency, the way his sister nearly was, is the series’ it factor.

The result is a genuinely endearing series that balances adult relationship messiness with a romance that never feels forced or overly serious. It treats falling in love like a scenic walk rather than a sprint, and that slow, earnest pacing is exactly where the manga shines.

While Marriage Toxin reads like manga’s answer to Hitch, the series also shares a pretty funny source of inspiration with Naruto.  More specifically, bug user Shino Aburame. In an interview with Manga Passion, Joumyaku revealed that the series setting was inspired by Masashi Kishimoto’s formative shonen manga and how romance, an otherwise tacked-on thing in it and other shonen, would be handled amid all its fighting and clan building.

“Many people struggle with the bug-controlling profession, but since it’s been passed down through generations in the family, I wondered what the ‘marriage search’ might have been like. I thought it would be interesting to make a project out of that,†Joymyaku told Manga Passion. “However, since bugs as protagonists might put many people off, I chose a poison user as the main character, as poison is the closest equivalent.â€

Fair enough! And as far as Gero’s marriage search goes, I’m partial to the sardonic goth queen Makoto Himi by virtue of being Nana-pilled, but I’m ultimately a Gerosaki shipper. And given Kinosaki is also Joumyaku’s favorite character, I’ll continue to cope with them being endgame.

What’s nice about Marriage Toxin is that the series is a fun, engrossing read on Manga Plus, and it’s got an anime adaptation in the wings by Bones Film, the same studio behind Gachiakuta, My Hero Academia, My Hero Academia: Vigilantes, and Fullmetal Alchemist creator Hiromu Arakawa’s upcoming anime adaptation of Daemons of the Shadow Realm. Translation: the show looks like it’ll have the juice across the board in its action, character acting, and animation quality when it begins streaming sometime this April.

Want more io9 news? Check out when to expect the latest Marvel, Star Wars, and Star Trek releases, what’s next for the DC Universe on film and TV, and everything you need to know about the future of Doctor Who.