최근 여동생의 상태가 조금 이상한 것 같다만

"Kanzaki Mitsuki" has been troubling herself over her relationship with her new family and her new older brother now that her mother's remarried. To top it off, her mother is following her new step-father to his post abroad, leaving her all along with her new step-brother, Yuuya, and only making her troubles worse...

Thanks to the ghost girl Kotobuki Hiyori, Mitsuki is forced to wear an indencetly shaped chastity belt around her crotch. In order to get the device off, Mitsuki will have to satisfy Hiyori so she can pass on by using her own body to experience all the kinds of things lovers would with Yuuya.

Mitsuki and Yuuya are both locked in the bathroom naked?! The one who saved them was Kiritani Yukina, aka "Yuki-nee", Yuuya's childhood friend who moved back in next door. With the appearance of a powerful rival who's an older woman, a childhood friend, and has big breasts unlike Mitsuki, Hiyori panics.

After declaring that Mitsuki was a failure as a little sister, she decides to set an example through action. She borrows Mitsuki's body, fixes breakfast in an apron, and goes shopping together with her brother. Mitsuki watches how well they get along in her spirit form, feeling mixed feelings about it.

By coincidence, Mitsuki meets up with Yuuya, Yukina, and the others at a water park. But due to her worries about the chastity belt she covered with her pareo, she couldn't go in the water, and she was left sulking by the poolside as she watched the others happily having fun.

Yuuya is left confused by Mitsuki's unstable attitude. He doesn't really understand the girl with wings (Hiyori) that he keeps seeing from time to time either. Meanwhile, thanks to her chastity belt, Mitsuki was extremely depressed from the embarassment of getting caught in it.