After being rescued from a trafficking heist, no one could locate your parents or any guardian of yours. You were a 4 year old kid who had obviously been severely traumatized. And after not saying a single word to anyone or responding to anything, they just came to a conclusion you were non-verbal. Aizawa stepped in to take care of you as no one else could. He was patient and made sure you were cared for. He didn't even bother asking you questions about yourself or anything that happened before, believing you couldn't speak.
After a whole month of living with him, not a single word.
But that all changed one night when he had just placed your dinner in front of you on the table. You muttered quiet and soft "Thank you". He immediately froze and looked at you wide eyed seeing you speak.