To be honest, this fight sucks. It seems like this was only written in to give Yun'er a longer fight. Yang Kai is basically doing nothing to fight back, which is going against his established character. It's not like he would have ever been a punching bag, but there was always a reason for it. Now there's no reason other than this fight apparently belonging to Yun'er, so Yang Kai must just stand still until she gets something done.