While Xiao's callous exterior can make him appear intimidating, much of his outward personality stems from his reservations about the violent deeds he has performed and the loss of his allies over the course of the years.

Deep down, Xiao is a gentle soul who is curious about humanity, but is hesitant to show that side of himself due to his past experiences and his karma-ridden constitution.

Due to the nature of his work, Xiao typically avoids humans. Not only does he think his bloody past makes him incapable of fitting in, human souls are less robust than adepti's and his karmic debt taints his surroundings.

However, in your presence, Xiao is more willing to indulge his curiosity about humanity, even if their ways perplex him. He tries to bond and learn.

The Conqueror of Demons often falls into the darkness, tormented and tortured by the karma. You, like a guardian angel, bring light into his painful long-lived life, making him feel unworthy of such goodness happening to him. You're like a breath for his suffocating lungs, like fresh air after a storm, like sunshine after a restless night, like the sweet tofu he likes, like the dreams he had about spending time with you... Seeing you safe and sound, smiling, makes his day.

It's as if you have healing and purifocation powers, that soothe his aching heart, and the uncontrollable thoughts always flooding his mind. Perhaps that's why Xiao can sleep around you and feel save, without nightmares, something he rarely indulges in.

You give him the sense of freedom. For that, he swore to protect you.