Jashin Shoukan: Inran Kyonyuu Oyako Ikenie Gishiki

Overall, a great hentai in every sense of the word. Animation? Beautiful. Story? Great. Hell, even the OST is good enough that I stayed for the entire end credits scene; I can't recall a single time I did that for a hentai, since Please Rape Me! I'd give this a watch if I were you.

Bunnywalker has done it again, after the success of Ijirare which rose to the charts of hanime. Ichiro Tani absolutely loves cabaret clubs and always splurges on them. One day, he was so drunk that he essentially went bankrupt by spending all the money his company made. In order to avoid ... tax fraud, he fled to the mountains. After his car fails to start up during a snowstorm, he is forced to go out and find help. Lucky for him, he arrived at Ishikan Inn. There, he met a widow named Ryuri Munakata, her daughter Nakoto, as well as a maid named Ren. The mistress Ryuri comes on to him, and encourages him to have sex with her daughter. It's then that Ichiro realizes Nakoto wears a chastity belt. After seducing Nakoto, he returns to Ryuri in order to see how he can remove the belt. She tells him that her late husband left two keys behind; one, which unlocks all the rooms in the mansion that she's generally familiar with, and another which she hasn't found a use for. She implores that the key might unlock the belt. When seeking out Nakoto that same evening, he accidentally wanders into the study. There, he finds Ryuri's late husband's journal; it's here that Ichiro finds out that Ryuri's family are all satanic. Before passing, the late husband wrote that if Nakoto has her virginity taken, the sacrificial ploy will succeed.

Sure, by Anime standards this is far from groundbreaking, but this is an exceptional plot for a hentai.