Pink no Curtain

Based on the same-name erotic slice-of-life manga by George Akiyama, serialized in Weekly Manga Goraku.

Virgin boy Okuyama is a stocker at the supermarket who has no luck with women. His life is thrown upside down when his sister Noriko unexpectedly moves into his house. Okuyama is overcome with lustful thoughts for her, but she regards him simply as a brother.