Immoral Sisters - Season 2 Episode 2 Entangled in Sisterly Love (2004)
Kunihiko's furious when he finds out about Taketo's relationships with his daughters, but it turns out he's got some secrets of his own - like how he's been lusting after Tomoko for years. When she finally makes a move on him, he can't resist, and they end up having sex... Kunihiko's wracked with guilt afterwards, but then Yukie and the others propose that they all just start sleeping together to make things easier...