It's a ComicFesta hentai with two versions: a "standard version" (3-minute episodes, for TV) and an explicit "complete version" (7 minutes with sex scenes, for online streaming). Unusually, both versions have the same voice actors. Anyway, I watched the latter.
Compared with hentai, it's pretty good. It's wholesome, vanilla and sometimes funny. It's not incest, because they're not blood siblings. Everyone's happy and there's no rape, strange kinky stuff or other non-consentual activity.
By non-porn standards, though, it's disappointing. Three pseudo-siblings have sex. This drives dramatic and comedic tension, since the two sisters (Ayane and Kotone) don't know they're both shagging Kazushi. We follow their misadventures, waiting to see how it'll get resolved... and it doesn't. There's no revelation. No one tells all and no one walks in on anyone else. It's a status quo. Kazushi's going to keep doing this, cheating on both sisters and having dangerous sex that must surely be found out sooner or later. (Kotone even said in ep.6 that she was happy with being Girl #2 if Kazushi was also seeing someone else, making it even more painful that he's keeping it all secret.)
In other words, it's a non-story. It's a good premise, but they've forgotten to give it an ending.
That said, though, the dangerous sex can be pretty explosive. I'd be pausing in agony every so often, although the situations aren't always convincing. I don't believe for a moment that Ayane couldn't hear Kazushi and Kotone through that flimsy door in ep.1, for instance, while the siblings' sleeping arrangements in ep.2 are absurdly contrived. Firstly, they all sleep in the same bed. Uh-huh. Secondly, the girls wear hoodies so that Kazushi can't see their faces, thus setting up a terrifying moment of mistaken identity. Yikes. I don't believe it, but holy shit.
Result: Kazushi and Ayane have sex in the same bed as a sleeping Kotone. They run a similarly insane risk in ep.5, when they're hiding in the girls' locker room at school and Kazushi starts frigging Ayane while four other girls are in there, changing.
(Yes, school. Kazushi is at university, but Ayane and Kotone are at high school.)
The show delivers the porn goods. Boobs are huge and there are a few eye-catching outfits (naked apron in ep.7, swimsuits in ep.8).
I don't mind the implausibility. It's hentai. I had low expectations. (It is often silly, though, e.g. when Ayane goes off to look for clothes for a topless Kotone in ep.8 when her bikini top's floating in front of them in the water. I was also surprised by the line about Ayane's swimsuit being revealing, when Kotone's dressed as an indecent exposure waiting to happen.) The episodes are daft, but startling. No, what I object to is the non-ending. If they fixed that (or if they released a Season 2), I'd regard this series a lot more positively.