Kaisara

Kaisara is the het ship between Kai Satou and Sara Chidouin from the Your Turn To Die fandom.

Chapter 1, Part 1
On the night of the kidnapping, Kai hurriedly tried to warn Sara not to go home. However, she and Joe thought he was a stalker and ran in fear.

After Sara saves the others from Russian Roulette, he thanks Sara last. He explains that she is no ordinary high-schooler and that she shouldn't overwork herself. Sara begins to question Kai why he voted for Q-taro rather than her, and then she remembers that Kai is the person who was trying to reach her that night.

Chapter 1, Part 2
After Joe's execution in the Main Game, Kai uses the knife from the kitchen to commit suicide. He tells Sara that the moments she spent letting Miley mock her gave him enough time to do what he needed to and that his suicide is his feeble resistance. He entrusts Sara his hopes and regrets before collapsing and expiring.

Later is revealed he and Joe were acting together to protect Sara.

Chapter 2, Part 1
In a flashback, Sara's father gives Kai a new apron, thanking him for his service. Her father entrusts Sara to Kai, should it come to it. Kai ensures she has his protection and affection. Sara's father begins to lose himself, misunderstanding Kai's good intentions, and Kai comments that he has a bit of tunnel vision when it comes to his Sara.

Later, when the survivors find his laptop, Sara realizes that Kai was never a stalker and that he was guarding her to protect her from the kidnappers. She remembers what she heard from him the night she and Joe were kidnapped-- “Don't go home.”

Chapter 2, Part 2
Checking the laptop again, they find several messages from Kai, some files, and computer code. There's even a file detailing all of Sara's likes. In one of the files, titled “To Miss Sara”, Kai reveals he was raised as an assassin. He was tasked with protecting Sara from the shadows. He implies that the Death Game could be revolving around Sara herself, though he believes she is but a victim as well. He admits the organization he worked for is named ASU-NARO, startling Q-Taro, who says that was the name of his orphanage. They're the ones who had kidnapped the participants. He directs Sara to a folder titled after her.

In the Sara folder, there are two files. The first is a letter to Sara thanking her and her family.

General
Even though Kai was participating in the Death Game, he associated with the group that organized it. He was trained to be an assassin, and he infiltrated the Chidouin household as a homemaker in order to get close to them and set the Death Game into play.

While working for the Chidouin family, he developed a soft and caring side for them, particularly for Sara, and decided to go against his group. He attempted to stop the Death Game from starting up, or at least protect Sara but ended up failing.

Fanon
While Kaisara is somewhat popular in the Japanese fandom, it's still controversial in Western fandom spaces due to the age difference between the two characters despite the fact it's allegedly smaller than Keisara's age gap.

Fandom
FAN FICTION

PIXIV
 * Kaisara tag on Pixiv