This review may contain spoilers. I can handle the truth.
The only reason the “redeemed abuser” angle doesn’t break it is because Ishida’s behavior started and stopped when he was a rather young child. Obviously that doesn’t make it okay, but where the genuine ability to change is important, young children are really the only characters that can work.
Ueno is interesting in her supremely abject naiveté and the fact that she responds to everything genuinely, despite her lack of tact or ability to do even simple things right.