Raku Ichijou is the sole heir to a yakuza family. Ten years ago, Raku made a promise to his childhood friend. Now, all he has to go on is a pendant with a lock, which can only be unlocked with the key which the girl took with her when they parted. Now, years later, Raku has grown into a teenager, and all he wants is to remain uninvolved in his yakuza background. However, when an American gang invades his family's turf, Raku is to pretend that he is in a relationship with the daughter of the gang's chief, so as to reduce the friction between the two groups. Unfortunately, the girl is convinced he is a pathetic pushover, and in Raku's eyes, she is like a savage gorilla. Nisekoi follows the daily antics of this mismatched couple who have been forced to get along. With many more girls popping up his life, all involved with Raku's past somehow, his search for the girl who holds his heart and his promise leads him in more unexpected directions than he expects.

Despite having seemingly quelled the war between their respective gangs, Raku Ichijou and Chitoge Kirisaki still carry on with their fake relationship. Eventually, as Chitoge's perception of Raku slowly changes, she even begins to see him as a little charming. Chitoge struggles to come to terms with her newfound feelings for Raku, as a new girl joins the slew of Raku's admirers and the competition among those vying for the yakuza heir's attention grows even fiercer. And amidst all this, Raku's search for his first love and the contents of the mysterious sealed locket continues in Nisekoi:, which picks up where the first season left off.