godan verb (-ru), intransitive verb
reform oneself; improve one's conduct; straighten up
Used when a person's behavior or character becomes better, often after a period of misbehavior. Implies moral or social improvement from within.
彼は最近、素行が修まってきた。
His behavior has been improving lately.
あの不良少年も
That delinquent boy has now completely reformed himself.