If you think Overflow's synopsis sounds like the manhwa hentai called "My Brother Slipped Inside Me In A Bathtub" don't worry about whether your subconscious is dirty, because this anime really is adapted from that hentai.
Overflow’s story is a basic hentai story: Our MC bangs his sisters. Actually not his real sisters. These girls are his childhood friends (don’t believe it, they’re actually our MC’s cousins but anime takes it more softly), occasionally they visit MC’s house for sleepovers, and one of these days an accident happens between MC and his cousi--- I mean his childhood friends, Ayane and Kotone. After that day, MC gets into relationships with Ayane and Kotone but our girls don’t know that MC has relationships with both of them. Although this situation causes some thrilling scenes, it does not really have a big effect on the plot.
We have three main characters in Overflow: Ayane, Kotone, and Kazushi.
Kazushi is our MC who bangs his childhood friends and he's a big jerk. Ayane and Kotone really love him but he is playing with this naive girls’ hearts just for banging them.
I called Ayane and Kotone as “naive girls” but actually the only naive one is Ayane. Kotone is just a straight nympho bitch who would still bang with him even if she knows Kazushi is in a relationship with her sister. On the other hand, Ayane has really a decent personality. She banging with Kazushi because she thinks Kazushi (her crush) loves her and I'm sure she would never forgive Kazushi if she knew he was in a relationship with Kotone too. That’s why I liked Ayane more than Kotone…
Just kidding, I liked Ayane more because I prefer brown hairs over black hairs.
It’s just another low-budget hentai show. The visuals are good but the animations are so bad. Also, there’s still mosaics even in the complete version.
If you've already read the manhwa version of Overflow, the only reason to watch this adaptation is voice actings.
Voice actings aren’t that good in general but voice actings in +18 scenes are great. However, it would be inconvenient to go into details and explain why voice actings are great in these scenes, so I'm skipping that part.
This was a mediocre hentai to watch. It was nice to see the locker room scene with voices and animations but I’m a little bit sad about that they didn't adapt the pudding scene (a.k.a best sex scene in this series). If you want to watch a hentai where the MC bangs his thick cousins, Overflow is a good choice.