It's the rule of comic book hero showdowns. They fight each other for spurious reasons when anyone halfway sane would have talked it out, both land decent hits on each other so they can both look cool, then something comes along to make them stop fighting or team up or go eat lunch or something. That way they can make the fans argue with each other which one is cooler or "really won" instead of having irate fans bitch at them for making their favorite character look weak.
Maru-yu-san is older and wiser Gouta's Shigure is, most of the time, machine of destruction that steamrolled everything on her path with look of indifference Or best described as "meaningless act of violence" for the victims