very over the top, on Shouta's part, but then again that's also sorta a logical path & conclusion for that type of character personality when they're pushed to the edge like this.
the taser felt like a bit of a leap, but it sells the potential danger she was in. And, Satou was there, so Koharu was ultimately going to be safe.
I will happily admit to enjoying the expression in the final panel. "Yes, yes, NTR this & that", but I will always applaud comeuppance, specifically.