Xiao Muli followed the mercenaries out for training, and Situ Xin, worried about his safety, had asked the people of The Dark Division to keep an eye on him. It was precisely because Situ Xin asked The Dark Division to pay a little attention to Xiao Muli.
That she learned about the various experiences he had while out with the mercenaries. There was danger, there was difficulty. Yet, Xiao Muli had toughed it out.
While on a mission with the mercenaries, during a critical moment, Xiao Muli risked his own injury to save three members of the mercenary team. And it was precisely because of this act that the mercenary team truly accepted him, even though he wasn't one of their own.