Nisekoi

As a child, Raku Ichijo made a secret promise with his childhood sweetheart, keeping a pendant as a memento while his love took the key. He dreams of one day meeting his past love, but years later, reality smashes his hopes when Chitoge Kirisaki accidentally knees him in the face...
Though Raku's a normal high schooler, his family heads the notorious yakuza gang the Shuei-Gumi faction! And he's dragged into family affairs when he's forced into a relationship with Chitoge, the daughter of a rival gang's boss!
Despite their constant spats, the two somehow fool everyone with their false relationship. Raku then discovers that Chitoge has a mysterious key from her past, which she can't remember... Plus, two other girls appear with keys as well—Kosaki Onodera and Marika Tachibana!
Caught in the midst of this love maelstrom, even more complications arise for Raku when his class decides on Romeo and Juliet as the class's play for the school festival. Can the two false lovebirds pull off the impossible and make the play a success?
(Source: VIZ Media)