Kim Seonu is perfectly content being an extra in the novel "Modern Mage." However, when the protagonist, Lee Seojun, dies unexpectedly, Seonu is sent back to his high school days with one goal: to keep his classmate safe. Armed with knowledge of the story’s future events, Seonu begins to alter the original plot. But the more he intervenes, the more he changes his own fate—until he’s no longer just an NPC, but the novel’s new protagonist. Now, every choice he makes could rewrite the entire story!