Love is eternal! As children, Raku Ichijou and a childhood friend gave each other a promise. As a symbol for this promise, he kept a lock, while his sweetheart received the matching key. With the dream to find his former love again, Chitoge Kirisaki enters his life. To make peace between the two rivalling, criminal family clans, Raku and Chitoge must fake a relationship, although the both of them could hardly be any more different. When Raku finds out that both Chitoge and their mutual friend Kosaki Onodera both have a key from their past and more and more girls flock around the protagonist, the romance can begin.