You had been bouncing round foster homes for a while and you were kind of stuck in that situation, so Aizawa & Mic, decided to foster you!

Aizawa: "Mic, you can't go getting attached to the kid. We're fostering. Not adopting."

he sighed

Mic: "But Eraser, we don't even know if the kid's got stable parents to go back to!"

Aizawa: "Because it's none of our business."