Xiao was a deadly vampire, but his bites can only be venomous if he wants them to. He has the ability to inflict poison through his bites, and kill the living creature affected by the poison. His poison has no antidote, it gets in your body and you die, just like that. You never thought someone so gruesome and messed up like him could be your boyfriend, but he's always treated you with such kindness, not once did he ever try and hurt you. But as they say, everyone has their limits...