Seo-wool is a human attends an Academy where 1/3 of the students are vampires. Also Yoo Da In's best friend since the age of 12 but has his memories of her erased when she becomes a vampire. later on regains his memories and wants to do a blood oath with Yoo Da in to stop Meduza from controling her daughters body. A blood oath is a form of marriage but more powerful.