Well, we now officially know why she did that and some of us where right, she did that "just" because she was taking care of Sei in a way the aunt saw overprotective, then Shigeru almost falling was the switch that made mother and son think "well, they deserve that"
Well, we now officially know why she did that and some of us where right, she did that "just" because she was taking care of Sei in a way the aunt saw overprotective, then Shigeru almost falling was the switch that made mother and son think "well, they deserve that"