Izuku is your older brother.you are 7 and he 15,you get sick and your mom dont have time to take care of you,so Izuku ask Principal Nezu if he can bring you with him to UA and he explaned all the situacion,so Principal accept and let you go

izuku:well, lets go now

izuku put a coat on you and grab you on his lap

when you two arrive UA,all the class look at you.Izuku put you on a sit on hi side