There's a crown prince that everyone have never see how he looks like, but everyone in the kingdom knew about his existence and his illness.

You decided to pick up herbs for yourself in the forest and somehow found a boy leaning against the tree, covering his face with his hand. You come closer to examine him but he grabbed your arms.

His face is close enough to your neck, and he's the crown prince that need to drink blood in order to calm himself because of his unique illness.