#i'm using some of her manga canon characteristics and extrapolating a fair bit about her

[seriouslysexyflanders]

Of family,kidnappings, and "The Needs of The Many vs The Needs of The Few"

Sayu Yagami's life was turned upside down when she was kidnapped by foreign criminals. A valuable hostage in exchange for a supernatural weapon - the one used by Kira in his realm of terror,no less. It was a killing notebook,according to what she heard from the foreign criminals(she wasn't fluent in English).

The situation was beyond bleak - either she would die by one of the mobsters(so much for ending crime,Kira. His/Her realm was pristine on the surface,but the rot was just better hidden. She knew very well about a neat surface masking putrid layers - a lot of the mean girls she dealt with were class representatives with high grades and popularity among the other students. Sayu herself often had to use her own clout to help some of their targets - it was difficult to do so without harming herself socially), or a bunch of gangsters would get a supernatural WMD. Sayu couldn't decide which scenario was the worst. And considering L(supposedly the World's Greatest Detective) was in charge of the Kira Case,her chances of surviving the ordeal were pretty low. All became Sayu was too busy swooning over her crush to pay attention to her surroundings.

When Sayu Yagami braced herself to deal with her imminent death,her father arrived with the evil notebook. The exchange was made. Her father felt like a failure because he exchanged the safety and lives of countless people just so his daughter would live. Being reminded of her mistake was like getting shot in the heart,and she readily apologized for being too distracted. She was reassured by her dad and,weirdly,by L himself(or herself,she didn't know). Those words had the expected effect.

------------------

In a span of a few months,Sayu lost both her father and brother to the Kira Case(Light,in particular,died to ensure Kira would get themselves killed as well). Not only that,but she struggled with her own emotions and had to take time off college while grieving,and also after the kidnappings. Still,Sayu decided to keep in touch with her friends and regularly hang out,isolating herself only made things worse. Those emotional wounds were harsh but very much survivable. Sayu Yagami still managed to graduate and even get a job soon after - her best friend,Katsumi Haruno,made sure of it. To top it all,her mother was also healing a little bit every day. She was much more of an introvert than Sayu was,but still had a solid support system in the form of her sisters. They didn't talk much,but their bond was undeniably strong even after years of distance.

But something couldn't get out of Sayu's mind:the very fact that her life was considered more important than keeping a WMD away from mobsters. Yes,her dad felt guilty over giving away the deadly notebook,and he was very influential in the NPA. However,there was a matter of L being okay with it and even comforting her after the fact. Many people made theories about who/what was L - a branch of some particularly powerful police/military force,an agency created by billionaire companies. All of them seemed reasonable before,but they wouldn't give away such power in exchange for a random civilian. Therefore,Sayu decided that the true L(or people acting like it) died in the middle of the Kira Case,and her dad and other NPA agents took over. But still,Sayu found odd that none of her father's coworkers urged him to call some police/military agency,ignoring the risk. That would've been the most logical choice. However,Sayu doesn't know if she'd be able to make such a decision if either Light or her parents were in such a situation.

Nevertheless,Sayu was absolutely sure Light would choose her life over keeping a WMD out of the criminals' hands. Not only because he was often a caring,protective brother towards her,but he was also fundamentally selfish and morally lazy. Whenever Sayu vented about bullies in her schools and how risky it was,Light simply advised her to ignore the issue. Sometimes, he was even condescending to her by calling her reckless and non-strategic,telling her to get more power to protect herself against retaliation(admittedly, good advice). The worst is that Light disliked bullying just as much as Sayu herself did but couldn't be bothered to actually fight such injustices. Not only that,but he was The Best Student of Japan™️,teacher's darling,and almost everyone seemed to like him.