He's a member of the national swim team who's been struggling with poor records. Hopes to be a top swimmer. As an Alpha, his physical condition could be improved by pairing with an Omega, but Xiao has a big fear of Omega pheromones. The smell of an omega makes him shake & throw up, so he avoids them at any cost. But, his condition got better after meeting you. You were an omega with scentless pheromones. He keeps you for purely practical reasons for his self-interest to help him get stronger.