Crazy theory what if Ao is actually the kid that left with the other girl in the boat to fix his eyesight back when peter was still a child not burn. And the supossed sister that we though had been killed by Nezumi is actually the other girl. Peter does not seem to recognize Ao but based on that one time they crossed in the door Ao does know him so would explain why he is surprise of seeing him there and why would he call him one of his friends. That or they just where made friends after meeting on the door for their mutual love for Nezumi