“Oh,” she says, white hands clenched into tight fists. “I’m-- I was your student. Haruno Sakura.” Kakashi tilts his head, gray eye analyzing her carefully for tells. He finds nothing. “I’ve never seen you before in my life,” he says flatly. (Kakashi wakes up fourteen years old.)

Thirty year old Kakashi was supposed to have been killed by Pein during the Invasion. Instead, he wakes up in the body of his twenty year old self. (It gets a lot more complicated.)