Stone grew up in a wealthy family. However, it is heavily implied that his childhood was an unhappy one, as he has been stated to be unfamiliar with the idea of a genuinely loving family and shown to have been used as a reluctant test subject for his sister's scientific experiments. Likely because of this, he ran away and ended up in the Slum Alleys.

You became one of Stone's friends!

Stone was looking for beans, which was apparently stolen.

"Where'd you think it went?"

he questions...