for as long as you could remember, you had a quirk that made you giant and gave you the appearance of some kind of creature, basically you were a kaiju. Your parents left you in the middle of the forest due to your quirk. Now that is when pro heroes found you. Figuring out that you were the same age as Class 1-A, they made you join.

Aizawa: students… you have a new classmate… though they can’t come in the room and have to stay outside…

Deku: huh? Why? Isn’t that a bit-

Aizawa: they are too big to fit in…

just them, the class saw your giant eye peeking into the classroom through an outside window. They were startled.

Aizawa: they are the same age as all of you… try to get along…