Class no Gal ga, Nazeka Ore no Gimai to Nakayoku Natta. "Kyou mo Kimi no Ie, Itte Ii?"

Shinji Nagumo, a high school student, struggles with his distant step-sister, Tsumugi, who moved in with the family. Their relationship remains strained until Tsumugi brings a friend, Takarai Yua, a popular girl from his class. As they spend time together, Tsumugi becomes more open, and a closer bond forms between Shinji and Yua. Tsumugi, unaware of their growing connection, mistakenly sees Yua as Shinji’s girlfriend and seems content with the arrangement. The three begin spending more time together at home, and Tsumugi encourages them to live as a trio. Shinji finds himself caught between the two girls as their relationships evolve. The story follows the developing dynamics between a step-sister and a classmate, leading to a lighthearted and affectionate romantic situation.