It's lovely. It's a happy, charming gender-bending show that I'm sure my children would have loved if I'd shown it to them. (Except that it has the odd scene and joke that's unsuitable for small children. Its hero has a massive pornographic game collection, schoolboys overreact to mildly naughty suggestions, etc. I made that mistake with Gonna be the Twin-Tail!!, which is silly and funny and my children were thoroughly enjoying it... until Tomoko objected to things like Twowearle trying to take Souji's virginity by clamping her mouth to his crotch, or the innocent-ish Erina being sent to buy pornography. Whoops. I'd forgotten about those bits.)
But I was talking about Onimai. If your age is in double digits, it's fine. There's nothing bad here and I'd happily recommend this to men, women and anyone in between.
Mind you, some Western commentators got upset about its portrayal of transgender issues. So by all means avoid this show if you think your buttons might get pressed by a silly anime about a teenager inventing a gender-switching potion and giving it to her brother. (Which was probably a good move. He'd been a lazy good-for-nothing who hadn't gone outdoors in two years and had no hobbies beyond masturbation. Frankly, anything would have been an improvement. Transforming him into a robot, brain-swapping him with a lizard... anything.)
Anyway, our hero(ine) is Mahiro. He's a man in a schoolgirl's body. (The sex-change potion also reduced his apparent age to maybe 14 years old or so.) He uses masculine pronouns and occasionally thinks he needs to reclaim his masculinity after catching himself doing something particularly girly, but to be honest he doesn't seem too fussed what form his body takes. He's fine with it. It's unclear which way he'll swing romantically when his body ages enough for that to become an issue, but for now he's almost scared of female nudity. (Although his sister Mihari doesn't count. No incest subtext in this anime.) He's more worried about all the peripheral stuff, e.g. going outdoors and talking to people. Let's face it. He'd hardly been a beacon of masculinity even before this. Mihari helps him deal with clothes, make-up, periods, etc. and he likes being cute.
There's enough closely observed detail that I was genuinely surprised to find that the original mangaka (Nekotofu) is male. I went looking and found an online interview that discusses this.
INTERVIEWER: Onimai's appeal lies not only in its tone and format but also in the depiction of issues unique to girls and its realistic portrayal of modern-day middle school kids. How do you achieve this realism?
NEKOTOFU: I gained all my knowledge by reading the great gender-bending works of the past, and Onimai contains a lot of that information. However, for really detailed, specific depictions like the process of washing hair, I use sources like a hairdresser's blog and other sources. I sometimes depict middle school students as they were in the past, but I usually try to make them fit into the present. For example, I might draw an episode about health checkups and not remember what they were like in my day. So I look them up, only to find that things are very different now. Since Mahiro is actually older than he looks in his new body, it’s a good opportunity to showcase that gap between my past and the present, too. It’s a very conveniently structured narrative for me.
The visuals are superb, yet on first glance might seem childish. The art style is rounded, cute and full of pastels. It's easy to draw, frankly, but that'll be a factor in the animation being superb. It's wonderfully fluid and the character acting is great.
The cast are equally lovable. Mihari is capable of being so happy that she cries at evidence of her brother turning into a human being. Their friends are all light and funny. There's nothing complicated about them, but they're fun to be with and you completely understand why Mahiro comes to value them more than having a penis. He even goes to school! This happens halfway through the season and makes the show scarier, because Mahiro can be dozy as hell and is capable of making you curl into a ball of pain that's saying "NO NO NO DON'T DO THAT". (Humans are weird and strangely designed.) This makes the show stronger too.
The main thing I disliked was the title sequence subtitles. They're liable to be different in every episode and quite a few of the options are obnoxious. Comparatively innocuous Japanese lyrics get turned into randomly chosen examples of much cruder English, or even internettisms ("gAwn!? heeR!?") The title sequence itself is charming and I like the song, but I should probably have turned off the subtitles for its duration.
The other thing that irritated me was ep.7. Mahiro is overconfident about his school exams. Okay, yes, but falling asleep in the exam room... piss off.
This show could have been creepy as hell had Mahiro started leching or ogling his new friends. He doesn't. He effectively becomes asexual, albeit with some effort and/or running away on his part. For now, being asexual is his goal. (The age reduction must be part of this.) He does, though, enjoy dressing up and being pretty. He might preen or fish for compliments. He's often an idiot with a catastrophic lack of appropriate girl instincts, but he's also engaging and relatable in a situation that was alien to me at least. (He also has strong character growth over the course of these twelve episodes.) If I'd been him, I'd have stayed in that body too. Charming friends, a social circle... what's not to like? At least compared with his previous life. I'm hoping for a second season!