Yuichiro is just a boy, around 12 years old when a deadly virus struck the earth, killing Everyone over 13.

He and his family, which was just a group of kids at an orphanage, all called themselves by the last name Hyakyua, because that was the name of the orphanage.

After the virus came only minutes later and entire army of vampires came, they took all of the children and forced them to live in the vampire and give them their blood under the farce that doing so would provide them with protection form the monsters which roamed outside.

Yuu never accepted it, and would do anything to go outside, unfortunately that same burning desire will cause him to loose everything... Or so he thought