AU (though not especially divergent as yet)
Spoilers through Chapter 38.
Part 1 of Road Not Taken
The evidence just wasn't adding up properly. He could see why Ryuuzaki had been suspicious of him - he could see why Ryuuzaki was insisting they be chained together twenty-four/seven. What he couldn't see was how any of it could possibly be true.
Kira... to be Kira, that was impossible. But why? Why would it be impossible? Raito's eyes narrowed. Because he had no memory? But L had already hypothesized that he and Misa (and if he was Kira then he had no doubt that she would be the second) had lost their memories somehow, perhaps in a transfer of power. This... there was not a zero percent chance of it being true. Raito knew this as well as Ryuuzaki did. So why had he immediately thought it impossible...?
"Yagami-kun? Are you all right?" Ryuuzaki's voice cut into Raito's thoughts, and he looked up, blinking. Owlish, tired eyes stared into his from no more than a few inches away.
"Aa." Raito nodded. "I'm thinking back over the case to this point."
"Ah, no wonder you looked so serious." Ryuuzaki pulled back and gave him his usual sickly grin. "You get very narrow eyes when you're thinking."
Sometimes, Raito speculated on the odds of Ryuuzaki dropping dead from malnutrition and him being called Kira for the death. That didn't seem to be quite zero percent, either. Fortunately, if the detective had lived this long on sugar and caffiene alone, he wasn't likely to die now. It would be a shame if Ryuuzaki died, after all - the man was clearly insane, but also absolutely brilliant. His mind was always working, always had the right answers.
Except for two. Kira and the second Kira.
"Do I?" Raito asked distantly.
"Mmhmm." Ryuuzaki regarded him over his teacup. "...you're starting to get bags under your eyes, like I have. This is a good thing, it means your brain is working harder. Soon you might even surpass me." Tea - so sugary it was nearly sludge in the cup - vanished into Ryuuzaki's mouth with a slurping noise.
"Nonsense, I just haven't been getting enough sleep." Raito reached up unconciously to rub his eyes. "I seem to be attached at the wrist to someone whose idea of sleeping is to blink three times in quick succession."
"Sleep dulls the mind," Ryuuzaki announced, then turned back to his own work, typing furiously with both hands as he held the edge of the cup between his teeth and continued to drink.
Shaking his head, Raito returned to his thoughts.