Ko and Shin Hizuki are two very special brothers. Shin was adopted by a vampire couple who two years later had a biological son, Ko. Therefore, between the two there is no blood bond but their relationship is very strong, despite Ko being a vampire in all respects, while Shin is a normal human. Their life was turned upside down when another vampire killed their parents, forcing Shin to make a "blood pact" with Ko, giving him his blood to protect him by making him stronger.