Volume 8 of Nisekoi ニセコイ a manga series written and illustrated by Naoshi Komi. It was first published in November of 2011.
The plot follows Raku Ichijo, a boy who wishes to study in a good university even though he is the son of a famous Yakuza. Raku has a necklace with a padlock shape that was given to him by a girl when he was just a little kid. This girl, promised him that they will see each other again as soon as he opens the padlock and Raku suspects that this girl might be one of his classmates.