Sayu Yagami

The manga series Death Note features an extensive cast of fictional characters designed by Takeshi Obata with their storylines created by Tsugumi Ohba.

In the fictional stories featured in the Death Note universe, Tsugumi Ohba, the story writer, created characters that lived in a world featuring a notebook in which names written on it would lead to the ones named to die, typically the cause of death being a heart attack when otherwise not specified. The story follows the novel of a character named Light Yagami, who uses the notebook he found in order to cleanse the world of those humans which he deemed unfit for society. A team of professional investigators set out to find out the mysterious killer and arrest him, and thus many other characters are introduced until Light is eventually caught. The story creator chose names for his characters in a way that, as he described, "seemed real but could not exist in the real world", due to the fact that most of the characters were criminals or victims. Light Yagami, the main character is depicted as the deadliest of them. Some character details differ between the manga and its anime, live-action film and drama adaptations.

Light Yagami (夜神 月, Yagami Raito^?) is a bored intellectual dissatisfied with the Japanese justice system. When he finds a Death Note dropped by Ryuk, he envisions to create a world without crime and rule over it as its "god". His alias Kira (キラ^?), derived from the English word killer, is quickly popularized and draws the attention of the Japanese police and L. Though initially sensitive to the pain of others, Light's descent into his role as Kira marks a dramatic change in his personality as he becomes comfortable with manipulating people's lives.

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Wikipedia