Episode list

The episode starts with 12 year-old Shion day dreaming and not paying attention during class. It's his birthday today so after school he heads over to his friend Safu's house to have a party with her and her grandmother. The storm outside starts to turn into a typhoon, so Shion heads home. Once home, he goes out on his balcony and screams. An alarm goes off inside so he heads back in. When he looks back at his window, a strange boy is standing there, who seems to be injured. After gaining the boy's trust, Shion proceeds to treat his wounds. We find out the boy's name is Nezumi ("Rat"). Shion discovers that Nezumi is a wanted fugitive - a VC - but he still aids Nezumi by giving him food and letting him sleep in his bed. The next day, Nezumi is gone and the Security Bureau arrive at Shion's home to question him about the situation.

After harboring a VC, Shion is stripped of his elite citizen privileges and forced to live in the suburbs with his mother. Four years later, Safu leaves him to go study abroad in No.5. While being with Safu, Shion comes in contact with a rat that had Nezumi's voice. While working at the park security, Shion learns of a mysterious parasite that makes people grow old and die in seconds before a wasp emerges from their necks. Shion questions the authority of the city once again after one of the deaths isn't shown on the news. Shion's co-worker also dies from the parasite shortly after and Shion is arrested. While being taken to the correctional facility, Shion is rescued by Nezumi and has to throw away his ID bracelet. After the duo escape from the city's limits, Nezumi shows Shion what really lies beyond the walls of No.6.

Soon after escaping from No.6, Shion finds that he is also infected by a parasitic wasp. However, his reaction is much slower than the others, and he screams for Nezumi to remove it from his neck. The parasite is extracted by Nezumi and he survives, but not without taking its toll on his body: his hair is white, his eyes are red, and he has a red, snakelike scar coiling around his body. After recovering, Shion is taken by Nezumi to a hotel whose owner, Dog Keeper, rents dogs to keep the guests warm while sleeping. Shion finds that Nezumi contacted his mother and she sent a message to him. By analyzing the parasite, Shion concludes that when spring comes, a large number of them will emerge and kill their hosts, causing turmoil in the city. He predicts that the Holy Day will be the day all the parasites become active. By learning that such great tragedy will befall the place he loathes, Nezumi rejoices. When Shion states that the inhabitants of No.6 must be warned, Nezumi claims that if he insists in helping them even after he learns the truth, the two will become enemies.

Following Shion's mother's instruction, Shion and Nezumi pay a visit to Rikiga, an old friend of hers. When asked how he knew Shion's mother, Rikiga states that Karan had turned him down when he asked her out. Rikiga offers himself to take care of Shion, but Shion himself gets angry on him when he asks Nezumi to work for him as a male prostitute and the two leave. While cleaning Dog Keeper's dogs, Shion is inquired by her about his relationship with Nezumi, and when an angry Nezumi appears before him, she realizes he became attached to Shion. Believing Nezumi became soft because of Shion, Dog Keeper attacks Nezumi with her dogs, but their fight is interrupted when Shion arrives. Shion confesses to Nezumi that despite caring for his mother, he decides to live in the West Block with him, and has one of Nezumi's rats send a farewell message to his mother.

Another person in No.6 has suddenly aged and died, this time a woman who worked at the Twilight House that Safu's grandmother is staying in. Shion hears about this from Rikiga and races to the theater where Nezumi is performing to inform him of the news. But during the play, Nezumi has a vision of a strange wind and song and he faints on stage. Meanwhile, in an art museum in No.5, Safu is looking at a work which displays three wasps when she, like Nezumi, is visited by a strange wind and song, and she also faints. When Safu wakes up, she is told she must immediately return to No.6 because her grandmother has died.

Safu has returned to No.6 because of her grandmothers' death. After she collects the last of her grandmother's things, she realizes that something is odd when her grandmother's knitting needles are missing. She also observes that the clothes left by her grandmother don't smell like her. While back in No.6, she visits Karan and learns of what has happened to Shion. After leaving Karan's bakery, Safu is abducted by the security bureau. Meanwhile, Shion and Nezumi continue their discussion over the future of No.6 and the parasite wasps. Nezumi receives a notice from Shion's mother informing him that Safu was taken by city officials. Nezumi contemplates whether or not to tell Shion as he would die trying to save her, but in the end, he decides to keep it a secret from Shion.

Nezumi secretly requests that Inukashi obtain information on the correctional facility, giving a large sum of money as payment along with the promise to sing if Dog Keeper were to die. However, unbeknownst to Nezumi, Shion and Rikiga are visiting a used clothing store where Shion discovers Safu's coat that was smuggled from the correctional facility. Meanwhile, Safu is being treated as a "sample" by the researchers at the facility where she was taken. That night when Nezumi comes home, he sees that Shion has made a large supper. The two eat and Shion says he was happy to have met Nezumi before giving him a "goodnight kiss", his way of saying goodbye. The next morning, Shion tries to leave to go to the correctional facility, but Nezumi catches up to him. The two fight before they promise not to lie to each other anymore. Nezumi tells Shion that there's something he needs to show him.

In order to save Safu, Shion and Nezumi head to the edges of the Western District. There, they meet a legless old man who leads a large group of men. The old man, the person who named Nezumi, is actually one of the researchers with the young Karan in Rikiga's picture. The man tells Shion that he was the real first survivor of the parasitic wasps. He also states that Nezumi is the last survivor of the forest folk who were wiped out by No.6. After Nezumi has another vision with the winds and the singing like he had before while he was performing in his play, he repeats the song to the legless man and the water around them begins to glow. The legless man tells them about Elyurias, the reason No.6 destroyed the forest folk.

Holy Day is getting closer, and after gathering information about it, Rat, Shion, and Inukashi learn about some sort of cleansing operation that will take place. Meanwhile, the rumble of tanks breaks up the city wide celebration in the streets of No. 6...

Shion and Nezumi climb the huge pile of bodies where they were dropped in and infiltrate the facility searching for Safu. Meanwhile, Rikiga and Dog Keeper leave the baby Shion saved to one of the dogs and gain entry into the facility by themselves to clear a path for Shion and Nezumi. Somehow, Shion knows exactly where to go and where all the cameras are, and this makes Nezumi a bit suspicious. He and Shion fight their way through the complex until Nezumi is wounded by a security guard. Shion kills him in retaliation, much to Nezumi's grief. When the duo manage to get through Safu's location, they find that she broke herself free and the researchers around her are lying dead on the ground.

The Holy Day is finally here, and chaos soon erupts around No. 6.