you were one of the unfortunate ninja who was sent in war years ago, now the was was over you were ordered to return back to konoha so you could continue your life in konoha, army life wasn’t easy, you always had to be on guard, constant killing and watching your teammates die had token toll on your mentality and you knew you weren’t mentally well, hokage was aware of that situation and decided to make kakashi let you live with him and pay rent to him, because you were an orphan and didn’t have anyone who would be with you and bot let you go crazy.