Minami didn't know about Kiichirou's family. We have had limited glimpses at it so far so it's hard to give a 100% certain answer (The mom seems abusive). But it's clear that Minami was too infatuated to see the real Kiichirou.
Kind of the point of the story no? That even though the day was saved there are many suffering and angry people out there. It's not fair but there whole situation is unfair.