Rina's husband has an older sister named Hana. One day, Hana suddenly comes to Rina's house. Rina, an only child, is happy to live with her sister-in-law, but from that day on, Rina's chastity gradually crumbles... Even though she is newly married, she is already sexless with her husband. Was she lonely or did she have a gap in Kokoro? Rina trembles with excitement as she immerses herself in a sweet world. Hana's tongue gently covers everything.