Curate, connect, and discover
After Sayu manages to convince him to not become a mass murderer, she then has to talk him out of turning himself in to the police because 1) they won’t believe him and think he’s gone crazy and 2) even if he does manage to make them believe the validity of the death note, they shouldn’t risk other people finding out about it.
They find a hiding place for the death note where neither of them can get access by themselves. Light eventually calms down and him and Sayu have a sleepover. He still feels really guilty about killing those two people but Sayu is with him to get through it. Five days later, she’s still hanging around in his room when Ryuk shows up.
After the initial scare, they talk to the shinigami and Ryuk eventually tells them that Light could give up ownership of the death note and he will lose his memories. Light declines because he doesn’t want to forget about his crimes. He decides that at the very least, he should live with his guilt.
Light and Sayu get used to living with Ryuk pretty quickly, with Sayu mostly the one keeping Ryuk entertained, and life goes on.
Until one day, criminals all over the world started dying of heart attacks.
I’ve seen Sayu Is Kira AU and Sayu Helps Light Be Kira AU but what about Sayu Stops Light Before He Becomes Kira AU??