Sekaiichi Hatsukoi Episode 0.

Hatori and Yoshino have been going out for a year now, and Hatori reflects over that. Yoshino gets a call from his mother who complains over how he never visits. As Hatori plans to go to his parents’ house, Yoshino decides to go along with him and visit his mother and sister. While there, Mrs Yoshino makes a remark how Hatori and Chinatsu (Yoshino's sister) would make a nice couple, which makes Yoshino jealous. Hatori is touched by how much Yoshino cares for him.