|Tsukiko Sagi, a shy character designer who created the immensely popular pink dog Maromi, finds herself under pressure to repeat her success. As she walks home that night, she is attacked by an elementary school boy on inline skates. Two police detectives, Keiichi Ikari and Mitsuhiro Maniwa, are assigned to the case. They suspect that Tsukiko is lying about the attack, until they receive word of a second victim.
Soon the attacker, dubbed Lil' Slugger (Shōnen Bat in Japanese, meaning "Bat Boy") is blamed for a series of street assaults in Tokyo. None of the victims can recall the boy's face and only three distinct details are left in their memories: golden inline skates, a baseball cap, and the weapon: a bent golden baseball bat. Ikari and Maniwa set out to track down the perpetrator and put an end to his crimes. Their hunt is unsuccessful, however, and the investigation eventually leads to both men losing their positions as police detectives.
As the attacks continue, it is revealed that they are not random. Instead, Lil' Slugger seems to target people in crisis, and the attacks, though violent, lead to some improvement in the life of the victim. Maniwa becomes convinced that Lil' Slugger is a supernatural force, driven to rescue the desperate from their tragedies through violence. He becomes obsessive, broadcasting his warning about Lil' Slugger via shortwave radio and seeking a way to kill the supernatural assailant.
As public fear of Lil' Slugger intensifies, so do his (supposed) attacks, and the line between truth and fiction become blurred. At the same time, public anticipation for the launch of the Maromi television series reaches a fanatical high, almost as if the fear of one is feeding (and feeding off) the anticipation for the other.
Things come to an end on the night that the Maromi show is set to air. Ikari, now a private security guard, and Maniwa, now a wandering "knight," attempt to battle Lil' Slugger, now an incredibly powerful force. They confront Tsukiko, and she confesses that Maromi was based on a real puppy that Tsukiko had in childhood, whose leash she had one day accidentally dropped, allowing the puppy to run into traffic where it was killed. Instead of taking responsibility for the puppy's death, young Tsukiko invented a story about a bat-wielding, skate-wearing puppy killer—Lil' Slugger's first "attack."
Ultimately, Lil' Slugger is a paranormal figment of Tsukiko's guilt and fear, brought inexplicably to life when the adult Tsukiko desperately needed to escape her responsibilities and then fed and nurtured by the fear of the populace. In a way, Tsukiko does fulfill her job by creating a character (Lil' Slugger) that becomes just as big a sensation as Maromi. When Tsukiko finally confesses the truth, and in doing so accepts the guilt for the death of Maromi, Lil' Slugger is defeated.