IKR! just kick up behind u and land one in the balls or elbow em Σ(っ°Д °;)っ
I honestly think it's a cultural thing.
If this happened on my city, the groper would be puched in the face, for sure.
I guess it's natural thing to beat the shit out of such a pervert, but I also think some people in this kind of situation can be too shocked and ashamed to even react. I suppose it's the matter of character (in real life), but as you said in a manga it has some other reasons ;)
look at that bubble butt hehe
but on another note WHY DO THE CHARACTERS JUST LET THEMSELVES GET GROPED ON TRAINS LIKE I GET THE SEME RESCUES THEM BUT WTTFFFF