Historical

Story will become clear when the past is explained: a boy who holds a demon survives a massacre, his village is destroyed and burned to the ground. He is found by a priest (Sui twin-brother of the crown prince). At first the boy only craves warmth, but eventually he craves blood and sex. Sui will be devoured. When the other priests find Sui attacked they want to execute the boy. Sui saves him by making a pact.
Sui becomes a vessel to protect, but rivalling politicians are using him to attack.