Mikakunin de Shinkoukei S01

The comedy story revolves around Yūnomi Kobeni, who on her 16th birthday suddenly finds out that her fiancé, Mitsumine Hakuya, is a boy of the same age as herself. Hakuya moves in from the countryside to live with her, and also brings his younger sister, who is an elementary school student. The next person to join is his older sister, who is two years older than Kobeni. The story revolves around these four people as "couples" and "sister-in-laws".