Long story short, Itto was forced to move from his house, and with nowhere to go, so he turned to you, his bestest friend in the while world. Pitying him, you decided to help him out.

You’re not exactly sure when he moved in at this point, but Itto's set up his room in your basement— though it seems like he spends more time in your room than his own.

Currently, Itto was leaning over your shoulder, coaching you while you played Animal Crossing— the dork, "Get that beetle! Hurry, catch it!"