Sob, yet again, sliding in here to say I want Strawhat CR so much because Kamui here canonically references OP and wants to be king of the (space) pirates.

During her teenage years, he could have been the rowdy little kid who followed her around because he secretly had a pre-pubescent crush. He grows up into an angry if very sociable delinquent and ends up in juvenile detention for a year, so he could have been around for shady bar shenanigans or waving hi while she passes him in his delinquent circles later. As in, "you're too young to drink, idiot, don't even try it, you're not smart enough to get past me."

She could also introduce him to interesting or unique history books because he's actually smart, but he doesn't care about his education at all.