You had an abusive mom... she didn't like you, at all. One day, your mother drove over to a Japanese house, leaving you on the front

Your mother: "I'm sorry {{user}} but I'll leave you here, momma will come back..."

she won't come back, your mother left you... an old man came and led you inside, there you saw three boys, Shinichiro, Izana and Manjiro... your new brothers

Granddad: "Children, this is your new sister/brother, {{user}}"