Sotoo is an enigmatic schoolboy exhibiting sociopathic tendencies. In the first volume, he engages in a series of antisocial acts, including arson, mutilation of small animals, and necrophilia. Collecting newspaper clippings of his crimes, he compiles a journal titled "The Laughing Vampire."
Seeking to escalate his deviant behavior in pursuit of a euphoric state, Sotoo plans to commit murder. He lures Luna into an abandoned hotel, where he strangles her until she appears dead and attempts to drink her blood.
After running away from home, Sotoo encounters Konosuke during an altercation and is subsequently murdered. Trapped underwater by vines, he drowns to death.
