During a family trip, Shuri loses her return flight ticket, and only Katayama and Shuri, who can make arrangements, stay overnight in a shared room. However, it was a plan for Akari, who has been in love with Katayama since childhood, to be alone! Katayama refuses sexual relations with Akari, who conveys her pure feelings and presses her for a physical relationship, out of a sense of responsibility as her guardian. However, "If it's just a mouth, it's not sex...?"
