Even without Kumi, Ippo is also held back by he idea if he gets injured he'd leave his mother all alone. What Ippo has to learn to come back is a level of selfishness to pursue your dreams despite the risks.
One the one hand, I get what everyone is feeling. On the other, this does set up one hell of a rematch - BUT WE'RE GONNA HAVE TO WAIT AGES FOR IT DAMMMITTTTTT
I think it's gonna be... funnier. MC could wonder if kissing family would count, and asks to kiss his sister to test it out.
It's pretty normal but then when they ACTUALLY kiss, his sister AWAKENS.
I think it's a deadline for a "flag", in dating sims once you have enough flags you're on a route.
Maybe if he doesn't get a flag by the deadline he'll lose his powers and enhanced appearance and go to a BAD END or Common No Girl Route.
So, I'm not sure when that law became prevalent but also, iirc, oreimo never OUTRIGHT says they get together.
Honestly, it's probably a case of people just not wanting to risk it, and those that do are like "no way they'll hit me with this"