Anime Review TV and Film

Onimai: I’m Now Your Sister! – Series Review | Best of Winter 2023

Starting as a 2017 manga by Nekotofu, Onimai: I’m Now Your Sister! (Onii-chan wa Oshimai!) has been brought to life for the Winter 2023 anime season.

Even for a ‘gender-bender’ comedy, Onimai launched to quite a lot of controversy. A number of early critic impressions were incredibly negative, despite the series having a lot of fans and user ratings being high. Some viewers enjoy it but will give a rather unrealistic account of it; If you check the fan wikis for the series, you can see one example of this in stretched interpretations and statements that go directly against what the source material says written as if they were facts. This is echoed throughout fan discussions all over the Internet. It might make you wonder – just what is going on with Onimai?

As a disclaimer, I refer to Mahiro as he/him in this review, as he consistently refers to himself as a male.

Onimai: I'm Now Your Sister! - Mihari Dragging Mashiro

I’m Now Your Sister?

Onimai: I’m Now Your Sister! follows Mahiro Oyama, a young adult male, who finds himself being transformed into a girl that appears to be of middle school age. His genius younger sister created a drug to do this and slipped it to him, as part of her ‘rehabilitation plan’ for her older brother who stays holed up in his room all day.

As the series goes on, Mahiro is encouraged by his sister Mihari to leave his room and slowly rejoin society. It uses many of the normal tropes along the way, with the chaos of Mahiro’s first period, changing room problems, and other comedic moments caused by his having temporarily transformed into a girl. While he’s troubled by the problems, he takes the transformation itself very lightly, seemingly not caring too much that he’s not physically a male.

Onimai: I'm Now Your Sister! - School Life

One major difference to similar anime is the age factor. As the series goes on, part of integrating back into society means going back to school which he dropped out of previously. He meets new friends, who help him to start coming out of his shell.

The whole idea of rehabilitation through being drugged and suddenly changed into a girl is quite a silly one, but there are serious elements in the background. The reason for Mahiro secluding himself in his room, problems engaging with society, and what friends and family can do for us are all topics seen here.

New Years

Lighthearted and (Mostly) Wholesome

Although it has serious moments, most of Onimai comes off as a slice of life anime. With the anime showing little fun moments like meeting someone when out shopping, and the quest to get some anime goods, it’s also showing growth that contributes to the overall goal. Especially in the first half of the anime, they’re building Mahiro back up into someone who can go outside again.

We get to see some particularly touching moments between Mahiro and his sister, only made possible because of the transformation. His new friends have a great dynamic too, and time spent with them is always fun, following the ‘cute girls do cute things’ formula. I particularly liked the relationship with his new friend Momiji – it’s rather cute how jealous she gets. Her constant support for him is sweet too. Momiji’s own ‘boyish’ behavior and appearance are used well at points to subvert expectations too. It’s great comedy with wholesome moments along the way; not what you might expect going into this anime.

With all this said, I think Onimai is best experienced without overthinking it. There are plenty of points where it would raise questions if thinking too hard, including how they get Mahiro into school suddenly, or the morality of not telling others that he’s actually older and male but spending time with middle school girls.

Onimai: I'm Now Your Sister! - Kaede Fanservice

Fanservice and Age

Despite being surprisingly wholesome overall, the anime version of Onimai: I’m Now Your Sister! contains more fanservice than some will be comfortable with. It mostly limits this to the older characters, particularly often focusing on the busty gyaru high-schooler Kaede, but does include Mahiro quite often, who appears very young even when considering his real age, and occasionally does include the younger characters. The opening and eyecatches are some of the most severe examples of this. The international release has censored some of these elements, using cuts showing background shots instead, zooms, and techniques such as thicker steam than the original that obscures most detail. The angles used in certain shots or situations like accidentality hitting Kaede’s boobs (which give a very detailed jiggle) are certainly present though. Unsurprisingly for the type of series, it also has quite a few ‘not quite yuri’ moments.

On the bathroom topic, watching Onimai makes me suspect that the author has a pee fetish (they’d probably enjoy Otome*Domain). Encounters when using the toilet or people wetting themselves come up more than a couple of times.

In terms of tone though, I felt that while Onimai included many fanservice elements, it was mostly for comedic purposes and it never went so far that it detracted from the experience. Mahiro is usually cajoled by his sister if needing to do anything such as going into the women’s side at the bathhouse, and he mostly ignores the nudity of others aside from some embarrassment at times. It would’ve been very easy to make him a pervert who takes advantage of his transformation, especially as he’s known to play 18+ adult games, but they fortunately didn’t take this route. He’s surprisingly pure.

If the fanservice does bother you, I recommend reading the manga instead. Kodansha USA have published six volumes of it currently, and it’s a lot tamer while still keeping most other things the same.

The Trans Interpretation

The other major controversy is around the transgender interpretation. Onimai: I’m Now Your Sister! is not a serious story about coming to terms with gender identity and who you really are – it falls more into the gender-bender comedy category, much like Ranma ½, Gonna be the Twin-Tail!!, or Kämpfer. As such, there are aspects that some may feel uncomfortable with due to not being handled sensitively. For example, an early joke that has Mahiro take interest in yaoi content (which he later confirms he isn’t interested in) or his sister pushing him into wearing feminine clothes. While Onimai shows a lot of positive outcomes of his unexpected transformation, it doesn’t handle the concept of gender identity seriously.

A more positive interpretation is that there are a lot of themes in Onimai that may feel relatable to an individual transitioning. Mahiro is accepted as a girl, starts to feel more comfortable with himself, experiments with a more feminine appearance, and has a better life after the transformation. An element of wish fulfillment is there too, for a sudden transformation, along with the standard ‘redo life, but better’ wish that anyone can relate to. Mahiro’s new life isn’t ideal, but he’s shown as extremely fortunate in his friends and new experiences.

Anecdotally, a friend of mine once told me that Ranma ½ helped her come to terms with her own identity. It’s not the purpose, but I think that some good can still come of these types of anime. People will have their own opinion on this topic and how they feel about it. There doesn’t seem to be a clear consensus among the trans community or others sensitive to this topic, though there are certainly strong feelings both ways. Regardless, it’s worth being clear that Mahiro consistently sees himself as a male and talks of reclaiming his masculinity, even as he tries (and sometimes enjoys) dresses, feminine hairstyles, and lip gloss. Above all though, it’s worth remembering that this is meant to be a comedy and not taken too seriously or related to real world issues.

Animation and Audio

Onimai: I’m Now Your Sister! was produced by Studio Bind, who are extremely well-regarded for their work on Mushoku Tensei. Unlike their previous work, it doesn’t have any big moments that blew me away, but the animation is certainly high-quality throughout and the attention to detail absolutely stands out. It’s extremely well animated and this particularly shows in the ways that characters express themselves.

The music is great too. It’s true for the ending and background tracks, but the opening song ‘Identeitei Meltdown’ is extremely catchy and stands out in particular.

The main voice actors aren’t an all-star cast, but each has a lot of experience mostly playing supporting characters. I felt that they brought the characters to life perfectly.

Onimai: I'm Now Your Sister! as AOTS


There are some uncomfortable elements to Onimai: I’m Now Your Sister! and it certainly won’t be for everyone. Even so, it was my favorite seasonal anime for Winter 2023. Despite going a little overboard with the fanservice, it remained a wholesome anime, with great character dynamics, plenty of comedy, some touching moments, and showed an interesting journey of leaving the life of a NEET through a big change in life.


The anime of Onimai: I’m Now Your Sister can be found on Crunchyroll.

If you enjoy anime and the theme of crossdressing or gender-changes, you may be interested in our review of Otome*Domain or X-Change R.

If you’d like to see more articles from us, please remember to follow us on Twitter🐦 and consider turning notifications on. Or type in your E-mail address and click the button for free email updates. You can also come chat with us on Discord.

Support High-Quality And Detailed Coverage

Want to support the cost of us bringing you these articles or just buy us a coffee for a job well done? Click the Ko-fi button below. You can even find some digital goodies in our shop~!