Looking at how his dad rarely go home, there a chance the plot need him to move to another place, maybe his dad work related because that the only thing i see, unless author gonna be a dick and kill one of them
I mean it's possible.. The Dad would work away from home and rarely come back.. but if I recall, he made it a point that he'd be able to be home more often or something..
I could see Kaoru getting sick and missing the cultural festival.. could get what his Mom had, and at least there's a cure for it but it could cause hospitalization perhaps.
Either way, let's just hope it's just a scare tactic, and at most.. that one of them just got a cold or somethin' and instead of going to the cultural festival together, the healthy one decided to spend their time nursing the sick one.
Yup, Imma go with that thought. It's much happier even though it sucks.
Damn author and being ominous..