Sakura watches a boy burn people alive with blue fire from a bus window, then he shows up at her school the next day like nothing happened. The mystery of what he actually is, what he's actually doing, and whether she should be terrified or trust him never fully resolves, but the show doesn't care because it's too busy having fun with the contradiction. Government-sanctioned teenage assassins with elemental powers and a girl caught between turning him in and falling for him is the entire appeal, and the show knows exactly how dumb and entertaining that is.
Sakura witnesses something impossible: a boy standing calmly while blue flames consume people around him. The next morning, she returns to find the scene completely erased, no bodies or evidence remaining. When a transfer student named Rei appears in her classroom, she recognizes him instantly. He moves through school with an unsettling indifference, one black glove on his left hand, operating under a code that justifies killing with killing. Rei is a Code Breaker, a person who officially doesn't exist. He eliminates criminals using their own methods as punishment, operating outside all law and morality. Sakura becomes convinced that his path of endless violence is wrong, and she won't accept that murder can ever be justified. Determined to reach whatever humanity lies beneath his cold exterior, she positions herself as his unlikely opposition. What unfolds is a collision between absolute conviction and brutal pragmatism, wrapped in action and dark humor. Sakura's relentless optimism clashes with Rei's detached cruelty, creating an unlikely dynamic that questions whether anyone, even a killer, can be saved.