Then you must do your duty until the end. You did a great job and your sister is at peace knowing that you are a responsible guardian for her daughter.
Yeah, I'd like to change an anime story. I'd like to change the story of AoT. The titans are never created, they never exist, and everyone lives peacefully in their cities without any problems. There is harmony and prosperity everywhere in those regions.
I think "the scum" need rehabilitation and redemption, not punishment. I hold the belief that most people do evil because they have had traumatic upbringings and are emotionally hurt. It is very unlikely for people to just choose to do evil if they don't lack anything.