So Kiryu is definitely a Nice Adult but he's got a life of crime in his regains so I think it'd be totally hilarious for him to try and be a Good Influence but then wind up pulled into her schemes.

I'm not 100% sure how they would have met but part of me wants to say she is totally free to have mugged him (he was not a buff dude once upon a time) because honestly Kiryu would get mugged by a teenager, he'd just let her steal from him, probably.