Saikin, Imouto no Yousu ga Chotto Okashiinda ga.

Mitsuki, a high school girl, has a new older brother after her mother remarries a divorced man with a son. When her mother and stepfather move abroad, Mitsuki is left alone with her stepbrother, Yuuya, with whom she has little connection. One day, a spirit named Hiyori inhabits Mitsuki’s body and attempts to seduce Yuuya. Hiyori is a deceased girl unable to reach heaven and must complete a task to do so. She uses a device that activates when Mitsuki experiences sexual feelings toward Yuuya, helping Hiyori progress toward her goal. To remove Hiyori, Mitsuki must take provocative actions toward Yuuya, despite being only step siblings.