Fallen wolf, your cleansing has come.
~ Nemuru Kushinada

Nemuru Kushinada was a girl born in the town of Jouga-machi in 1968. Nemuru was the daughter of the town chairman. The town of Jouga, on the surface a normal town in the mountains, notable for growing hassaku fruit, and for tales of an endemic subspecies of wolves were said to inhabit the forests surrounding the town, the basis for a local goddess said to take the form of a "white wolf". In truth, however, the "wolves" were actually a metaphor for the behavior of the local inhabitants, who are referred to as kamibito, and are said to "both human and not human". It is implied that they may be a different subspecies of humans. The main features of kamibito are an enhanced sense of smell, superhuman strength and agility, and an innate attraction to certain humans, known as "Temptations" who emit a pheromone undetectable to normal humans, but irresistible to the kamibito. When exposed to the pheromone, and particularly, if they come into contact with bodily fluids of an individual who emits said pheromones, (typically by kissing or sexual contact, as the kamibito will literally "fall in love" with the emitter) they become addicted and prone to insanity and violence.

This was the world that Nemuru Kushinada was born into. As the sole daughter of the Kushinada clan, she was given the role of "Hunter", charged with assassinating "fallen wolves"- kamibito who made contact with the bodily fluids of a "Temptation" and were driven insane- in accordance with ancient religious laws of the town, which are secretly enforced to present day. Nemuru commits her murders at night, wearing a ritual outfit, most notably a wolf's mask, accompanied by other high-ranking kamibito, and kills the "fallen" with a large scythe. Nemuru is forced to accept this role, though she is severely psychologically effected by being forced to commit murder again and again.

After the protagonist, a boy named Hiroshi Kuzumi. Hiroshi is, though he does not initially know it, a powerful "Temptation"- people who emit the pheromone as strongly as he does are only about one in 100,000, which explains why the people of Jouga, both male and female, are highly attracted to him. This, along with the presence of at least one other powerful "Temptation" leads to Nemuru being forced to assassinate several people, one assassination is witnessed by Hiroshi. Nemuru eventually starts to question her role and eventually refuses to continue her duties, leading to the town leaders forcing her into house arrest.

Meanwhile, a doctor in town is working on a drug that would control the urges of the kamibito and render the town's current murderous system unnecessary. In a scene featuring the doctor, the anime introduces Shuuichiro Sakaki, a man posing as an employee of a pharmaceutical company. It is later revealed that Sakaki is in fact a hitman working for the town leaders, who want to assassinate Hiroshi, and is working with the doctor in order to get information on Hiroshi, claiming it is "data for research".

Nemuru hears the town leaders talking of their plot to have Sakaki assassinate Hiroshi- the ancient laws of Jouga prohibit them from assassinating "Temptations" directly, but they say nothing about soliciting their murder. Nemuru hears about this plot while locked in her room, and escapes house arrest, making his way to a construction site, where Sakaki is holding Hiroshi, and plans to execute him.

Nemuru escapes and makes her way to the construction site, determined to prevent Hiroshi's murder. At this point, it is revealed that Sakaki is not actually an assassin at all- he is a powerful "Temptation" who had is girlfriend murdered by Nemuru, who intends to take revenge for his girlfriend. Nemuru fights Sakaki, her superhuman strength initially giving her the upper hand, until Sakaki causes some debris to drop on her, knocking her out. Sakaki holds Nemuru in the same room as Hiroshi, intending to have Nemuru to be drawn to make contact with Hiroshi, before going insane and killing him. However, Nemuru resists the temptation and both are rescued.

Sakaki, however, escapes, and puts into motion a plot to cause chaos by releasing a "fallen" into the Hassaku Festival, where all the town would be attending, forcing Nemuru to kill the "fallen" in order to protect the rest of the town, revealing the murderous secrets of Jouga. In the chaos that ensues, Sakaki murders one of the town leaders with a switchblade, before he escapes, and heads for a dam upstream, armed with a switchblade and a revolver. Sakaki shoots one of the dam personnel and proceeds to open the floodgates, intending to flood Jouga and wipe out the entire town. The flooding causes some damage, but Nemuru and several other townspeople follow Sakaki and manage to close the floodgates before most of the town is destroyed.

Nemuru then confronts Sakaki on the other side of the dam, who points his pistol at the group. Nemuru admits to killing Sakaki's girlfriend, and offers to allow him to kill her if he would spare the lives of the rest of the town. Sakaki does not take the offer, and attempts return the dam, pointing the gun at anyone who would stop him. However, he is met by, Kaori Mana a girl who was his friend in college, who is actually a kamibito, who tries to stop him. Sakaki shoots Kaori, but with her last breath, she jumps off the cliff next to the dam, pulling Sakaki along with her.

Shortly after the incident, peace returns to Jouga, and Nemuru becomes close friends with Hiroshi and his two friends, two girls named Isuzu and Kaname. Nemuru and her father are seen discussing the progress made on the vaccine- in spite of the doctor being murdered by Sakaki, the work continued in the hands of others- which made the old system of assassination unnecessary.