Raku Ichijou, a first-year student at Bonyari High School, is the sole heir to an intimidating 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 typical teenager, and all he wants is to remain as uninvolved in his yak...