Night of the Ripper

The Night of the Ripper (リッパーナイト, Ripper Night) is the in-universe nickname for the conclusion of the second light novel and the Saika arc. In the story, it is the term used throughout the subsequent novels to refer to the night the mass-slashing attacks across Ikebukuro occurred and the terror of the serial slasher ended.

Synopsis
In the light novel, the event begins on the morning of the first Saturday in March, when Anri Sonohara wakes early and absentmindedly roams Ikebukuro, thinking about the rumors surrounding Takashi Nasujima and the former Raira student Haruna Niekawa. In the anime, it is a school day. On her way home, Anri is followed by Shuuji Niekawa, who attempts to attack her. Her stalker is noticed by Kyouhei Kadota and run over by Saburo Togusa. When Niekawa rises, seemingly unhurt, Celty Sturluson and Shizuo Heiwajima arrive, and the Saika-possessed Niekawa turns his attentions toward Shizuo and begins professing Saika's love. For the second day in a row, Shizuo beats him until he is unable to stand. Believing Izaya Orihara to be behind the latest trouble in the city, Shizuo leaves for Shinjuku to fight him.

Slashing attacks increase rapidly across Ikebukuro, and more than 50 people are caught up in the attacks and turned into children of Saika. That night, the chat room blows up as Saika continues to chant "mother," proclaim her love for Shizuo, and suggest a meeting place. Celty interrupts Shizuo and Izaya's fight and shows the chat logs to Shizuo, who arrives at South Ikebukuro Park to find an army of the possessed waiting for him, brandishing various blades and declaring their desire to cut him. Though he refuses their love, he welcomes a fight with them armed only with gloves made of Celty's shadows and no intention of holding back.

At the same time, Haruna Niekawa visits Anri's home to introduce herself and declare her intentions with Nasujima. The teacher knocks on Anri's door soon after, and Haruna chases the terrified man away, leaving some of her Saika children to kill Anri. Haruna is surprised and confused when Anri pursues her and protects the teacher she despises, and even more shocked when Anri pulls out the real Saika from her own arm. As Anri asserts herself and takes control of Haruna's inferior Saika, the children fighting Shizuo lose their will to fight and collapse.

Though badly cut, the lack of fear in Shizuo's heart keeps him from falling victim to the cursed blade's possession. He wins against the army and is gone by the time the police arrive. Casually walking home along a side street, Shizuo is confronted by a frightened and desperate Nasujima, who is seeking as easy victim to extort for money. Nasujima is quickly dispatched. The fighting puts an end to the serial slashing attacks that have been shaking Ikebukuro for months, but it eventually gives rise to the resurrection of the Yellow Scarves color gang.