Wait what?! Do NOT tell me other sister comes back or something?!
After hearing about this, if she does (try to) come back? It's only to cause strife. And it'd be a tempting target, too. Two of her favorite victims in one place, and in a position where she can cause horrible pain and anguish.
Now that Wakou knows beyond the shadow of a doubt what type of person his ex-wife is, he'll be on the defensive the moment she appears.
And on the subject of abuse....
....Man oh man, this doesn't just hit "close to home". For me, this one nails it right in the middle with all the horrifying accuracy of a Tomahawk cruise missile.
And then Wakou does the right thing. He wants her to tell him
everything. No matter how much it will hurt to hear, he knows she's gotta get it all out. This is what an abuse survivor needs to hear the most from their partner. "Tell me everything. I'm here for you."
MC is blessed.