As you know from the summary, this is a sequel to Death Note. Rather than the protagonist being a child of Light, this story is about the daughter of Sayu (Light's younger sister). Ryuk once again has dropped his Death Note in the Human World.
Years passed after the Kira Case had been solved. The task force had told Light's mother and Sayu that Light had died while trying to catch Kira rather than telling them the truth that Light was Kira. A few years later Sayu had married Near (real name Nate River but now Nate Yagami) and they had a girl who they named Yuki Yagami. She had her mother's brown hair that went a little below her shoulders and her father's black eyes. She was also intelligent like her uncle, though there were times when she struggled with new things in school like algebra. She was currently sixteen years old and a junior in high school. She often found herself wondering if there was anything she could do about all the crime in the world; the police never seemed to be able to catch all the most dangerous criminals, and lots of times people who were rich and famous were able to get away with crimes like murder. One day she was sitting outside her school reading a volume of Vampire Knight. Suddenly she felt something fall in her lap. She closed her book and looked to find a black book in her lap with Death Note written in white at the top. "Death Note," she read aloud," like a note book of death?" She opened it up to the first page which read: Death Note: How to use it. The human whose name is written in this note shall die. Yuki stared at the page, her eyes wide,"The note will not take effect unless the writer has the person's face in their mind while writing their name; therefore those who share the same name will not be affected." "This thing couldn't possibly be real," Yuki thought. But then she recalled the stories she'd heard of someone known as Kira who had mysterious powers that allowed him to kill someone if he knew their name and face. However he seemed to have disappeared years before Yuki was born. "There can't be much of a chance that this is real," she said to herself, "but I never throw away a book." She placed the note in her bag and headed to her next class wondering how the death note had gotten in her lap.
That evening Yuki was doing her homework but she couldn't stop staring at the Death Note and arguing with herself in her head. "Maybe I should test the death note to see if it's real. But then if it is real, I'll have killed someone-that would make me a murderer," she argued with herself. Finally she decided to take a walk to clear her mind. However while walking she saw in the distance a man with a knife walking up to a little boy from behind. He grabbed the boy and held a knife close to him. Yuki saw the boy start to cry but the man clapped a hand around his mouth. "I have to help him," Yuki thought and quickly pulled out the Death Note and a pen and opened the note to the rules: If the cause of death is not specified the person who's name is written will simply die of a heart attack within forty seconds." Yuki flipped to the next page. She recognized the man attacking the boy as a wanted criminal so thanks to that she knew his name. She scribbled it onto the page and waited looking at her watch, her heart pounding. When forty seconds passed, the man dropped the knife, clutched his chest, and collapsed to the ground. Shocked, the boy quickly ran off. Yuki stared at the Death Note, her eyes wide. "This has to be coincidence right?" she thought,"but he died exactly forty seconds after I wrote down his name. This means the Death Note must be real. Even though I killed someone, I did save that boy's life." She hurried back home, went up to her room, and opened the Death Note again. "If I was just able to save one person's life," Yuki thought," then I can save everyone; I can rid the world of all its criminals. Finally, a chance to bring people to justice!"
Throughout the week, Yuki wrote down the names of the most wanted criminals. She used different ways of killing because she thought just having all the criminals die of heart attacks would draw suspicion from the police since that seemed to have been what happened with the original Kira. Yuki mostly killed criminals who hadn't been caught. Murderers, poachers (because she cared about animals), bank robbers, and terrorists. At the end of the week, she looked at the names she had written down and grinned mischievously. "Seems that justice runs in the family," said a voice. Yuki turned around to see a tall creature with wings. He had pointy dark blue hair pointed straight up; a light blue face and neck; yellow eyes; a wide mouth with pointy teeth; and black wings, black legs, and a black body. Yuki's eyes opened wide at the sight of him. She stepped back a little. "Who are you?" she asked. "I am a Shinigami, a God of Death," he answered,"my name is Ryuk." Yuki held out the Death Note, "this must be your Death Note then. I was expecting you to come." Ryuk tilted his head. "Well, you are right; that Death Note used to be mine. But since you used it, it's yours now. You'd probably be interested to know that this is also the very Death Note used by the one you all call Kira." "Kira?" Yuki thought,"this is how Kira punished criminals?" She turned back to Ryuk, "if the Death Note belongs to me now, then why are you here?" "When a Death Note is used by a human, the Shinigami who previously owned it must stick by that person," Ryuk answered. Yuki shrugged,"okay, do you need to eat anything?" His eyes lit up,"I don't really need to but I love apples; got any apples?" Yuki looked at him, "first I need to ask you something; why did you choose me to own your Death Note? It fell right into my lap so you must have wanted me to find it." Ryuk grinned,"you're actually right; I was curious about how you would react to the Death Note and how you would use it. You see, besides the fact that this was the very Death Note used by Kira, he was also your uncle, Light Yagami." Yuki gasped,"I'm related to Kira?" she asked. "That's right," he answered,"so are you planning to kill all criminals and become the goddess of a new world?" She shook her head, "I do want to rid the world of criminals, but I don't really care about becoming a goddess as long as the world is clear of criminals. Sometimes I kill them by writing that one criminal killed another one, and then since his name is in the note, he dies as well. Hopefully that will keep the kills from looking too suspicious. All that matters to me right now is that I can make the world so much better and that I'm not caught doing all this." Ryuk's grin spread wide," Humans are just so interesting!"