Maybe I'm soft or too optimistic, but does Kippei really deserve this much of a retaliation for being dumb and indecisive? Karin, sure, but I feel like Kippei could've been a redeemable character.
I wouldn’t say being dumb and indecisive is his main problem. He’s married and he decide to cheat, which means he betrayed Aoi’s trust. It isn’t like where they first divorced and then he got closed to Karin soon after.
This isn’t some teenage romance where changing partners is normal. I know not all marriages last, but his marriage was stable. Yet because Karin is prettier, he became fixated on her and threw away all the memories and connections he had with Aoi. Now in the past few chapters the same happened, he cheated on Karin for Sumire Ito, who is pretty but all the good parts of Aoi, this guy is peak sleazebag.
At least his indecisiveness is a small saving grace since his first marriage never had a child. Imagine the trauma a kid would go through in this situation.
He already got his comeuppance by being mentally broken, but this divorce with Karin is still necessary in my opinion. Now he has nowhere to turn and will finally feel what Aoi went through after he cheated with Karin.
Even her own parents hated her and blamed her for the divorce. She had nobody to lean on, and now he’ll feel the same.
So far, no physical harm has been done directly from Aoi to Karin or Kippei, like stabbing or torture, so it’s still fine revenge to me.