Listen the mom is crazy but kosuke is actually and idiot and deserves to be reported. The dude is out here kissing an underage girl in her school uniform in the middle of a park .... what does he think would have happen? Even if it wasn’t Koto’s mom who caught them, what if someone who knew Koto or kosuke saw them??
As morally gross as it is, just wait a couple years until she turns of age