The reason was simple... she was sitting on Xie Qing's lap, who was casually smiling and stroking her stomach (this was a kind of request from the woman).
If you feel troubled, can I swap place with you? 😉
"Oh, damn it, I'm in trouble," Xie Qing thought, forgetting to wipe that disgusting satisfied smile from his face. Although he pretended to be a helpless sheep, his hands couldn't help but caress his older sister's body. He behaved shamelessly and calmed down only after examining all the parts of her body available to him at the moment.
"Damn. She wears such bold thongs under her clothes. As expected of the sect master!" he thought admiringly. Of course, after that, he put them away and didn't do anything strange. He was a pervert, not a horny animal... probably.