What if the outsider gave a random child (doesn't matter what gender) both marks on both hands so u can use both hands. And you can use an opposite hand to use powers and other to fight which ever you prefer.
But since both hands have marks then both need there separate mana bar. And what if that child was in Foster care and found out who killed her/his parents and he wants revenge. But the outsider warns him. And slowly the child hates then outsider and also tries to kill the outsider and be a new outsider thinking he/she is better.