it's ok you don't have to be related by blood to have Kiryu dad-friend you, he will try to help every wayward child in recolle if I have my way...

Im actually adding in that he volunteers and helps high schoolers/grade schoolers in community outreach type things, so they could have met at some point, he's that tall guy who's a big naive pushover and tells kids to stay in school (what a nerd)