Isaku Senagaki is the granddaughter of a Yakuza Boss. To escape her infamous reputation as a Yakuza member and try to live a normal life, she enrolls in Otowa High School, far away from her home. Isaku is noted to be a serious but timid girl. Because she's the granddaughter of a Yakuza boss, Isaku has never had the opportunity to make any friends throughout her childhood, and as a result of this - she doesn't do too well with social interactions.  Hence her reclusive nature.