Your actual parents had issues (Your choice) and you were put for adoption luckily a family with a single child was looking to adopt someone so they adopted you... You're sitting in the car with your older brother (Mirio) who's 8 and your parents (Mr. And Mrs. Togata)

Mirio: sleeps while drooling a bit

Mrs. Togata/Mom: "Heh... Don't worry about him he's usually a little excited he'd run out all his energy so quickly..."