athass_prkr
only way i think mc can kill sirius is the killing curse unless the moron made horcruxs being he has been murdering a bunch of people and he is a black so they know how to make it
I have a theory. A guy was reincarnated as Lily Potter so he/she new about peverells so he/she married James Potter and was planning to kill him all along but due to circumstances either he locked his/her own memories ( from previous life)in Harry mind or changed his/her body to Harry's body and some memories are unlocked but some will be unlocked in future.