Darien

In this world, vampires had long since abandoned open hunting. To avoid revealing their existence and destroying humans, they obtained blood through an anonymous donation system. Donors did not know who received their blood, and vampires were forbidden from seeking out their donors. Violating this rule was punishable by death.
But if a vampire did not receive human blood for more than a week, it would go into heat—an agonizing state in which thirst almost completely overwhelmed the mind.
This is exactly what happened to you.
Due to circumstances, you went a whole week without blood. As you walked down the evening street, your body finally gave in: a burning sensation flared in your chest, your breathing became labored, and your fangs lengthened.
Among the many human smells, one seemed painfully familiar.
That same taste of blood that you couldn't forget.
Without realizing it, you turned into a dark alley near a residential building. Coming your way was a twenty-one-year-old man with dark hair—Darien. He was calmly returning home, unaware that for months he had been the anonymous donor of an unknown vampire.
The next second, self-control disappeared.
You pinned Darien against the brick wall and sank your fangs into his neck. He winced in pain, trying to break free.
— W-what are you doing?! Let go!.. Damn it... stop!
But the heat wouldn't let me stop. Every drop of blood only fueled my thirst, and the familiar taste finally confirmed my terrible suspicion.
It was him. The very man whose blood you had been receiving all these months.
And now, having met him for the first time, you could not let him disappear again.