It's a mild hentai, if you've been watching the uncut 18+ episodes. (There's also an all-ages version.) There's regular sexual activity, but what they're doing is pretty tame and it only ever involves the same two people. There's nipple-sucking and fingering. That's all. Nothing more, except for the very last episode where they finally have full (and completely vanilla) sex. The bloke hardly ever even gets undressed.
It's based on an adult romance manga and it thinks it's light and romantic. What's more, it is. I enjoyed it. However there's also a consent issue that needs discussion, while in addition there's a lot of room for interpretation in the characters' sexuality and gender identities.
The plot's simple enough. Shizuka is a timid girl who tends to denigrate herself in conversation. She's scared of men, but she meets and gets on well with the beautiful, buxom Ryou. They're having nearly-sex as early as ep.1, but with a twist. Ryou's a cross-dressing man. He deceived Shizuka. The rest of the show is their evolving relationship, with Shizuka getting lots of reasons to be irritated, angry and/or happy (sometimes all at once) when she's with him. (She's not afraid, though. She'd always been scared of men, but he doesn't count.) Ryou is very keen on Shizuka and seems to be straightforwardly in love with her, right from ep.1, but Shizuka decides quite early that he's a terrible person.
The show's relationship with consent will probably kill it for some viewers. Ryou isn't very good at obeying when Shizuka says "no". I think he stops once, but there are other times when he clearly doesn't. What's more, he'll do it in public places, which is mortifying for Shizuka. Once was in a public toilet with people outside the cubicle asking if Shizuka was okay. (She'd been moaning.) Then, another time, they're standing in a crowded train!
Is this rape, or date rape? I think the answer to that is yes, at least sometimes. However, at the same time...
The first time they do it is okay, I think. She's the one who goes to his house and asks to be allowed to stay the night, after they'd spent all day together and showing us their romantically suggestive undertones. She then doesn't protest when he starts kissing and fondling her. Admittedly she's a bit drunk and startled by the cross-dressing thing, but we don't see her say "stop". She doesn't push him away or say anything to slow him down. Inside her head, admittedly, she's saying "no" and "this is wrong", but those are just inner thoughts and her lips don't move. The whole thing's dodgy, to say the least, and Ryou's guilty of not picking up on Shizuka's real feelings, but at least in this episode he's not yet gone too far.
Then, after that, she keeps meeting him! He'll bring her to orgasm and she'll protest, but then meet up the next day for another orgasm. They go on dates. They get on really well. She'll get angry or annoyed when he goes (way) too far, but it's the kind of anger that will disappear again in a moment. If they're out on a date, she won't even think of calling it off. Sometimes her exasperation is funny. (The nearest she gets to serious anger is at the end of ep.2, when she slaps Ryou and he's absolutely earned it... but even then they're soon back to usual.)
(Bizarrely, in ep.7, Ryou decides he's going to be a proper boyfriend and ask Shizuka's permission before doing anything sexual... and Shizuka tells him to go on as before.)
Right from the beginning, importantly, Shizuka both liked and fancied Ryou. She's attracted to both his male and female form, the latter potentially more so. Look at ep.1. "Even though she's a woman, I'm somehow getting attracted to her!" She asks if Ryou has a boyfriend "or something" and then blushes when s/he says no. Shizuka can also have her head turned by other pretty girls (e.g. ep.10) and of course she's always avoided men (although we can't read too much into that).
And then there's Ryou.
He's really into the cross-dressing, likes doing feminine things (clothes shopping, etc.) and seems to enjoy playing with gender. Admittedly he has a stated reason for his behaviour (to avoid female admirers), but he explains this as not wanting to be admired for his (male?) looks. He also seems uninterested in using his own penis, to the extent that Shizuka actually asks about it in ep.10. She'd been wondering if he was okay with, uh, always giving and never receiving. His response is just more fingerplay, which he says feels good for him. (They have full sex at the end in ep.12, though.)
That said, though, the show's aware of the darkness underneath. He's insecure about whether Shizuka would want to be with a cross-dresser and he gets downright scary in ep.11 after a misunderstanding. (That's not just my interpretation. Shizuka gets scared too.) That's only an undertone in someone who's basically happy, fun, super-sincere and playful, but it's still there.
The writing isn't perfect. There's a limit to what you can do in five-minute episodes that also have sex scenes. The last few episodes threatened to get eye-rolling with people being silly about their insecurities, although in fairness that turned out better than I'd expected. However there's one episode where I couldn't believe in Shizuka's underwritten anger. It's the one where they did it in a crowded train. It wasn't very subtle, either. Being quick to forgive is one thing, but I think you'd have to be some kind of fetishist not to go nuclear at being brought to orgasm against your will with that kind of audience.
Random observation: I laughed when Ryou and Shizuka went on a date to Something Theme Park. ("We have a theme!" "Great, what it is?" "Something!" "Uh...")
I enjoyed this show. It's funny and romantic, which was clearly the intention. Our protagonists are very likeable. However the show's nowhere near as vanilla as it thinks it is. You've got two people with unclear sexualities, testing the limits of consent in a way that Shizuka seems to be consenting to. If I took ep.6 literally, then I'd be seriously worried about her. Meanwhile Ryou might be a lesbian in a man's body, which was a joke of a university housemate of mine but seems a possibility here.
As hentai, it's nearly as tame as it gets. As adult romance, though, it's quite nice.