Slitterhead takes places in the 1990s in
Kowloon where mysterious monsters called Slitterheads are sighted killing humans. It starts with a spirit-like being called Hyoki possessing a dog and multiple people before defending a girl named Julee against a Slitterhead. Julee ends up being a Rarity, a person who not only remains conscious during possession, but has special powers and abilities when possessed. Julee gives Hyoki the name Night Owl, based on an old legend about two spirits named Night Owl and Leopard Head who fight the Slitterheads. After discovering that Night Owl has the ability to transfer knowledge and memories back in time, they start fighting major Slitterheads and recruiting other Rarities. However, they eventually encounter a Slitterhead with similar time powers to Night Owl. This Slitterhead torments the Rarity Alex, and starts to drive him insane with anger and hatred. This eventually starts to overwhelm Night Owl, causing a rift between him and Julee. Alex also kills the other Rarities, intending to forever punish himself with killing Slitterheads in the time loop. Julee is possessed by Leopard Head, another Hyoki, and attempts to stop Alex but is killed. However, Night Owl then transfers over to an alternate timeline where Alex was the one possessed by Leopard Head. It is eventually revealed both Night Owl and the Slitterheads are actually time travelers from an apocalyptic future. However, the travel process went wrong, resulting in the majority of travelers to turn into the parasitic race that are the Slitterheads. Night Owl is the only person who successfully traveled back, and Leopard Head is actually an alternate version of him. Night Owl then remembers he brought back a device similar to a mystic seal in case he encountered a foe he couldn't beat. After retrieving this seal, Night Owl returns to the original timeline to seal away the time manipulating Slitterhead and stop Alex's self destructive behavior. However, upon returning to the other timeline, it is revealed Alex has once again killed the other Rarities besides Julee. After Julee and Night owl win a final confrontation, Alex has Leopard Head forcefully crash a plane into the city. Rewinding time one last time, Night Owl has all the Rarities except Julee go into hiding before confronting Alex. This time, Night Owl possesses a person in the plane and manages to avert the crash. However, Alex's body quickly disappears. A post credits scene shows a possessed Alex driving off, with a message saying that the fight will continue into the next era. ==Development and marketing==