Synopsis from 'Saikin, imôto no yôsu ga chotto okashii n da ga.' Seisaku Iinkai: "Mitsuki has a new brother, Yûya, after their parents' remarriage. ¶ Mitsuki is having trouble adapting to her new life, but one day she meets the ghost girl Hiyori. 'I'm in love with your brother, but I died before I could be with him, and now I can't go to heaven.' And the only way for Hiyori to get to heaven is to make love to Yûya! ¶ Mitsuki is suddenly forced to wear the TST (a chastity belt). The heart-shaped gauge on the TST goes up whenever its wearer is feeling horny, and if it gets full, Hiyori can go to heaven. But if it gets empty, the person wearing it will die. In other words, if Mitsuki doesn't get horny for her brother... she will die! ¶ And there's also Yûya's old friend Yukina, who wants him for herself! What will happen to 'little sister' Mitsuki?"
