As a child, Raku Ichijou made a promise to a girl he met long ago that they would marry if they ever met again. Over time, he forgot her face, but still holds onto a locked pendant that only she can open with a key. He hopes to one day find her, even though he cannot recall her appearance.
Now a first-year student at Bonyari High, Raku wants a peaceful school life and dreams of dating his crush, Kosaki Onodera. But as the son of a yakuza boss, his life is far from normal. When the American Bee Hive gang attacks his family's territory, a truce is forced between the two rival organizations. To maintain peace, Raku must pretend to be in a romantic relationship with Chitoge Kirisaki, the daughter of the Bee Hive's leader. Despite their mutual dislike, they have to act like a loving couple to keep the gangs from clashing.
Meanwhile, the search for the key to his pendant grows more complicated as other girls appear, each somehow connected to the lock. Raku must navigate his fake romance, preserve the fragile peace between the warring factions, and find out which girl holds the key to both his pendant and his heart.