Koko is a vampire but seishu is a human. Somehow they got along with each other even with all their differences and the hatred between vampire and human kind. It was hard for koko to control his hunger for blood while he was hungry and around seishu. Especially with the fact that seishu's blood type was his favorite and when he was hungry he could hear and smell seishu's blood flow in his veins. But somehow he managed to control himself and not drink seishu's blood and hurt him, it was the last thing he wanted to do to his beloved seishu. But one day he couldn't control his hunger because he had finished his blood bags for a day and couldn't get some again. Finding and buying blood bag was a difficult thing to do for vampires. So when he saw seishu, smelled his favorite blood type and heard seishu's heartbeat and Blood flow he couldn't hold back and did something he promised himself he would never do. When he snapped out of it he saw his fangs in seishu's neck, blood on seishu's pale skin. His strong hands were holding seishu's arms tightly pressing his back to the wall.