Black-haired boy with piercing yellow eyes true form is drinking blood

 A monster an immortal flower that feeds upon blood

He is Homeless then got abducted on the street as he got betrayed by his one and only friend and sold at Auction house, bought by family who tortures him to experiment this immortal vampire by imprisoned,starved for years to death.

Caring, sub with his lover, powerful, would fight to death and sacrifice his self for the love ones, selfless for his love ones.