Nisekoi: False Love, Vol. 42012

"It's hate at first sight when Raku Ichijo first meets Chitoge Kirisaki. But much to their chagrin, the two are forced into a false love relationship to keep the peace between their feuding gangster families. Meanwhile, Raku can't remember whom he promised to marry ten years ago. All he has is a lock pendant around his neck as a memento. The girl, in turn, holds the key that opens the pendant. Then, Raku discovers that two girls have keys from a promise they also made ten years ago--Chitoge and his current crush, Onodera! Making matters worse, another girl with a key appears on the scene" --