Mitchaku kyonyû shimai: Oppai wa shitte iru

Original title: 密着巨乳姉妹　おっぱいは知っている

Saya is in love with her late sister Yoko's fiance, Masayuki. Yoko appears as an imaginary friend and encourages her, but she is unable to express her feelings to Masayuki. Masayuki begins dating a new lover, but...