Tomodachi no Onee-san to Inkya ga Koi wo Suru to Dou Naru no ka?

A high school student who considers himself unattractive and gloomy is frequently teased by his friend's older sister whenever he visits. She takes liberties such as drinking his beverages, entering his bathroom, and joining him under the blanket at night. Confused by her behavior, he asks a friend for insight but receives an unclear response. After losing a game, he is forced to comply with three of her wishes. Despite his uncertainty, he agrees, and over time, he may come to understand her true intentions. The story follows the evolving dynamic between this dense young man and the older sister who is unable to express her feelings openly, as they move toward a romantic relationship.