It's an incest anime. Some might even call it the definitive one. (There are plenty of others, but this is one of the strongest and best-known.) That label is a simplification and there's a lot more to the show than that... but incest is what it's famous for and the show knows it.

It's based on a 2008 visual novel, i.e. multiple choice adult computer game. The protagonist is Haruka Kasugano and the game has romantic routes for him with Kazuha Migiwa (refined heiress), Akira Amatsume (exuberant, bubbly shrine maiden), Nao Yorihime (childhood friend) and Sora Kasugano (his cranky twin sister). Yeah. Haruka and Sora have moved back to a town they lived in four years ago. They've just been orphaned after a car accident. They've got no one left but each other, while Sora suffers from ill health and a worse personality. She's obnoxious, needy and demanding. She initially refuses to go to school and would sooner spend all day net-surfing and eating junk food.

Ep.1 is fascinating. We've all been trained since childhood in reading drama and anticipating how things will turn out, but this first episode is unreadable. It has six-ish heroines who all think Haruka's hot and there are story routes for each of them. (Kozue's is only in a game fandisc and hasn't been animated here, but I loved the fact that she's in the anime anyway, gets as much focus as anyone in ep.1 and becomes important again in eps.11-12. As for Motoka's route, that's a series of twelve one-minute gag-and-porn minisodes after the end credits. They're funny, but I was startled to find that I'd been watching an entire bonus story route without realising. I promptly went back and rewatched.)

After that, the show does something I've never seen before. Critics called it a "vulgar version of Amagami SS", but that ignores the branching. (Incidentally, I like Amagami SS.) This series has this structure:

...and of course the mini-episodes of Motoka's arc follow each episode.

My watching order went as follows. Eps.1-6, what the hell, rewatch ep.1, which was extraordinary and I couldn't believe how much I'd missed on first viewing. I then did eps.7-9, then a rewatch of ep.7, followed by eps.10-12.

The arcs are linked. Kazuha's arc informs Akira's, as you'd expect from their relationship (spoilers). You'd be missing a lot if you tried watching Akira's arc on its own, which is ironically a bad showcase for Akira. (She's lovely because she's so energetic and enthusiastic, but that's not true when she's being clobbered with her own backstory.)

Those were fairly strong and I was enjoying the series, but then I hit Nao and Sora. Nao's arc is barely a gnat's wing away from being Sora's instead. They're intertwined, with Sora being jealous and a massive obstacle in both routes... and yet Nao's been suppressing four years of hating herself. In the end, it works out well. Then... whoah. Sora's route. I was scared from the start because Nao was surely going to get hurt. Ep.10 had me yelling at Haruka for not doing that stupid, stupid thing. Just tell the truth. Please. Now. (What's more, he'd been getting it right in ep.8.)

Terrifyingly, Haruka's still dating Nao and... oh dear. Ah. Okay. Yes, the siblings cross That Line, but it's only the middle of ep.11 and we still have an episode and a half of guaranteed catastrophe to go. I was in agony. I kept hitting "pause" to give myself time to recover and not scream.

Ultimately, it works out better than I'd feared. I was impressed with Haru for having a proper talk with Nao in ep.12. The anime got accused of "depicting incest as a socially acceptable act" by Japanese officials who presumably hadn't watched it, although charges were dropped.

This anime has a knack for cliffhangers. Oh my God. It also has some moments of idiot plotting, not necessarily excused by the brain failures associated with "teenagers plus sex". Why do Nao and Haruka hide in the pool changing room in ep.7? Admittedly they comment immediately on their own stupidity, but that's a writer's attempted saving throw rather than an explanation. Also, in ep.11... Right Next The Front Door. No no no no no no no.

The show's also steamy. This adds quite a lot of force. Clearly the producers decided that if they were going to cross the line, then they might as well cross it properly. It's by no means a hentai, but it has nudity, nipples and (non-explicit) sex scenes. It's capable of coming across as a study of female sexuality, in a way that the harem anime genre theoretically should be but never is.

It's a strong series. This should be pretty much a given with this subject matter, which can go for the audience's gag reflex in a similar fashion to cannibalism. In practice, though, incest has become fashionable in anime (albeit usually in less controversial forms like surprise step-siblings, not being blood related, etc.) and there's a lot of rubbish out there. This isn't one of those. I'd put it up there with Koi Kaze and Oreimo, although they're all very different shows. Admittedly the Motoka minisodes are silly and the second set of end credits is wallowing in fanservice and harem cliches, but everything else here is striking and memorable. (I liked the branching storytelling technique a lot too.)