Riding the bus one day, Sakura Sakurakouji looks out the window to see people being burned alive with a blue fire as a boy her age remains unharmed and stands over the people.
When she goes back to the site the next day, there are no corpses or evidence of any kind of murder, just a small fire.
When Sakura goes to class, she discovers the new transfer student is the same boy she saw the day before. Sakura soon learns that he is Rei Oogami, the sixth "Code: Breaker," a special type of assassin with a strange ability and a member of a secret organization that serves the government.
In short: Is this girl Sakura who see Ogami Rei - she hadn't knew him at the beggining - killing some people. She returns to the same place, and there she try to stop some bad boys to beat a homeless guy. Those guys try to rape her, and she is saved by Rei.
They become classmates, and she persuade him to not kill anymore.
Rei is a code breaker, a member in an organization who kills evil people. Some cannot be judged by the law, and in return they're judged by code breakers.
code breakers are in number of six - Rei is code breaker number 6.
Number 2 is Heike - he use light as his weapon. Apparently he was no eyebrowns, and he's a pervert.
Number 3 is Yuuki - his power is sound. He has a childlike nature, but he is the most violent - he hate the ones who destroy toys, especialy nyamaru. He's a very rich guy - he's the prsident of a toy company.
Number 4 is Toki - his power is magnetism. His eyes have different color, and he has a sister who doesn't remember him - she has different eyes too.
Number 5 is Prince (I forgot her real name) - her power is shadow, and she was an ex-breaker.
Number 6 is Ogami Rei - his power is blue flame at the beggining because with time his power would increase, and he would use other flames too, like the black on, called Belphegor.
I like other ex-breaker - I think they were call differently, don't remember exactly - Koujo and Yukihina.
When the codes uses their powers too much, they would lose them for 24 hours:
Yuuki - becames a cat
Heike - I do not know because he always wears an armor to hide his lost form, but apparently is hilarious.
Toki - became a child
Rei - is invisible
Prince - a mermaid
Kouji - a wolf
Yukihina - I do not know since it never show it
Sakura is a rare kind - code breakers powers have no effect on her, and when she use her powers too much she shrink. however she can be turned at her normal formed anytime if a special serum is used.