Synopsis: Saikin, Imouto no Yousu ga Chotto Okashiinda ga.

After her mother remarries a divorced man, high school student Kanzaki Mitsuki acquires an older stepbrother, Yuuya. Unfortunately, when Mitsuki's stepfather is transferred overseas and her mother follows him, she is compelled to live with Yuuya. Mitsuki feels isolated and estranged from her stepbrother, making it difficult for them to communicate with one another. One day, a ghost/angel named Hiyori appears and possesses Mitsuki's body. Hiyori is the deceased spirit of a girl who died before she could reach heaven and now seeks inner peace. Using a belt called TST, she tracks Mitsuki's sexual experiences with Yuuya, from dates to sex, and each time the belt fills up; she moves closer to heaven. To expel Hiyori's presence, Mitsuki must take daring and potentially unorthodox steps with her stepbrother.