I dont think you all understand. I wanted to see the author draw her getting slapped, cause I already know Ijin got revenge. In chapter 10 you see him close the Karaoke door with all the girls inside, like what they did to his sister so I'm assuming he didn't just give them a stern talking.
While Ijin does have a "code of honor" it doesnt include "not hitting girls". Also, they had already beat up his sister multiple times, so they were in fact hostile combative. If you attack someone should be prepared to get hit back. I just wish got to see it, cause the Blonde was the worst! Way worse than her brother, and we got to see him get taken down.