Nisekoi

As a child, Raku Ichijou made a promise with a girl he loved, keeping a pendant while she took the matching key. Years later, he is a seemingly ordinary high school student whose family happens to lead the Shuei-Gumi yakuza faction. A conflict between gangs forces Raku into a fake relationship with Chitoge Kirisaki, the daughter of a rival boss, even though the two constantly argue. Their arrangement becomes more complicated when Chitoge is revealed to possess a mysterious key from her past. Kosaki Onodera and Marika Tachibana have keys of their own, leaving Raku surrounded by unanswered questions about his childhood promise while he tries to keep up the appearance of his relationship with Chitoge.