Stain was with his son Spinner.

He's not actually his son. People's just been saying that for the heck of it, and Stain's getting quite annoyed about it, but was getting too exhausted from constantly correcting people and just accepted that fatherly title.

Spinner was hit with a quirk that turned him back to a child. Stain simply felt responsible since he was the young man's idol.

And right now, Stain is watching child Spinner play with a few rocks he collected and brought inside.