Onimai: I’m Now Your Sister!

Onimai: I’m Now Your Sister!

Onimai: I'm Now Your Sister! anime series cover art
Onimai: I’m Now Your Sister!

A Boring Premise Done Right

Onimai: I’m Now Your Sister! (Oniichan wa Oshimai! / お兄ちゃんはおしまい!) didn’t sound like it was going to be good. But, it turned out to be one of my favorite anime of the winter 2023 season.

The premise of the show is that a college-aged NEET is turned into a middle school girl by his younger sister. I don’t know about you, but that doesn’t sound all that interesting, to me. It’s not all that different from an isekai if you think about it. But, instead of a fantasy adventure, this is a “cute girls doing cute things” slice of life.

However, that’s a big part of why I thought this series was good in the end. Yes, it is a gender-swap anime and features various gags playing off that. But, at the end of the day, it’s a feel-good anime about cute girls.

Mahiro Oyama gaming from the anime series Onimai: I'm Now Your Sister!
Mahiro Oyama gaming

The picture above shows Mahiro in Episode 1, right after becoming a middle school girl. That’s a very different Mahiro than what we see her (him?) become later in the series. If Mahiro continued to be a male in a female body, the anime would have quickly gotten stale.

But, that’s not what happened. Mahiro grew as a character and eventually feels natural in her new body. Sure, we still got classic scenes of Mahiro freaking out about being in the girl’s locker room. However, that wasn’t really the main focus of the series.

Before Mahiro’s sudden transition, he had no job, wasn’t in school, and had no friends. But, by living as a normal middle school girl, Mahiro is able to make friends and enjoy life. If you’re on the fence about this series, try going into it with that in mind. It’s about making the most of life.

Main Characters

Mahiro Oyama is the protagonist of Onimai: I’m Now Your Sister! As I’ve already mentioned, Mahiro transitioned from male NEET to female middle schooler. But, this transition wasn’t by choice. If not for his sister, he would have continued his life as a self-proclaimed “home security guard.”

Mihari Oyama is Mahiro’s younger sister. Though, because Mihari is in high school, Mahiro is actually the younger sister now. Mihari is a scientist, which you can tell because she’s almost always wearing her lab coat. She developed a serum to turn her older brother into a girl.

Kaede Hozuki is Mihari’s friend. She’s a gyaru with an absolutely massive bust. In fact, the anime made her chest size even larger than it was in the manga. Kaede loves fashion and enjoys picking out outfits for Mihari, Mahiro, and Momiji. She’s also excellent at baking sweets.

Kaede, Momiji, Mahiro, and Mihari taking a selfie from the anime series Onimai: I'm Now Your Sister!
Kaede, Momiji, Mahiro, and Mihari taking a selfie

Momiji Hozuki is Kaede’s younger sister. She’s also the first friend Mahiro makes as a girl. Unlike her older sister, Momiji is tomboyish and is often mistaken for a boy. She feels much more comfortable in pants than in skirts or dresses. Momiji also gets jealous when others get close to Mahiro.

Asahi Ouka is one of Mahiro’s and Momiji’s friends from school. She’s your typical overly-energetic girl who can’t sit still and fails all her tests. I’m pretty sure Asahi mentioned having an older brother at some point in the series. But, we never see him.

Miyo Murosaki is the final main character. She’s the final member of Mahiro’s middle school friend group, along with Momiji and Asahi. Miyo is a quiet girl with a dark secret. She’s obsessed with yuri relationships. She reads yuri manga and enjoys seeing her friends in close contact with one another.

The Right Amount of Fan Service

Onimai has a fair bit of fan service. Actually, it has a lot of fan service. But, I never felt like it went overboard. Most of the ecchi fan service came from Kaede. However, even then, there wasn’t all that much of it.

The “most ecchi” fan service came when Mahiro, Mihari, and Kaede were shopping for swimsuits. Obviously, because of Kaede’s body type, this was bound to happen. But, considering the premise of the show, you’d expect there to be a lot more of this kind of fan service than there was.

I’m not going to pretend like there wasn’t other suggestive fan service, though. For example, there’s a scene of Kaede giving Mihari a full-body massage. And, of course, Mahiro goes into a changing room with Kaede and Mihari at one point. But, the majority of the fan service is the wholesome kind.

Mahiro, Kaede, and Momiji baking from the anime series Onimai: I'm Now Your Sister!
Mahiro, Kaede, and Momiji baking

What do I mean when I say wholesome fan service? I mean things like getting to see Mahiro and the other girls try on a variety of outfits. That kind of content isn’t sexual. However, it is still fan service. Who doesn’t want to see cute girls in cute outfits?

Something else that surprised me was the lack of sexual fan service directed at the young girls. There is some, and Mahiro is primarily the focus of it. But, there are also many times when rather than using sexual fan service, the series opts for comedy.

In one scene, Mahiro is freaking out because she’s in the girls’ locker room at school. She doesn’t know where to look because she doesn’t want to stare at the other girls changing. But, then she finds somewhere safe to look — at Momiji and Asahi because they’re completely flat.


In the end, I gave Onimai: I’m Now Your Sister! a 7/10. That’s actually lower than the average score for the show, which I’m a bit surprised by. I enjoyed this anime and it has very good production quality. It’s animated by Studio Bind, the studio behind Mushoku Tensei. But, I figured the content would have made people rate it lower.

And, not only do I think Onimai is a good anime, but it has a very good OP and ED. The OP for this series was one of my favorites of the season. And I’d say the ED is the definitive best ED of the season.

If you enjoyed this review, remember to click the like button down below. Also, follow me on your social media of choice — links are in the footer.

Finally, I’d like to thank Roman and JasonHK for supporting DoubleSama.com at the Heika tier this month. To learn more about how you too can become a supporter of this blog, check out Patreon.com/DoubleSama.

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