I think he's his *new* dad, like Harumi's mom just remarried. He said he'd only been his dad for a year.
Or he says it's only been a year cause he wasn't in the picture for some reason or another, Harumi does say he's his real dad.
I know this is old but what probably happened is his parents divorced when he was young and his mom remarried. When the incident of 'running away' happened, he was with his mom and step-dad but then he moved in with his real dad later to get away from all that.
Loved it and how couldn't they Know he was Harumis dad they look exactly alike! The first couple was stupid! tHe Blonde was stupider like why would you go out wih someone that likes u for someone else Literally But it made them Know their feelings and get back together!