Isourou Tengoku

Masahiko Kisugi, a high school student, is left behind in Japan when his parents relocate overseas, and he goes to live with Hitomi Mizuhara, his widowed aunt, along with her three daughters. Before long, Hitomi blackmails him into carrying on a secret affair with her, while her daughters Nozomi and Taki are also chasing after him at the same time. Once Hitomi learns of the web of concealed liaisons, she puts an end to the conflict by announcing that they will all share him. So that he does not fail out of school, the women reach an agreement to split up the days of the week, allotting Masahiko to each of them one day at a time.