Gin no Jeek
Jeekron, the silver jeek is a hunter of the dead in heaven. He's assigned by "the Law", the ruler of heaven to kill Marlord, the murderer who killed 200 teenager when he was still alive. For Marload's crime, he is punsihed by "the law" to reincarnated and died in his/her teen until the end of the humanity.
For this, Jeekron must trace Marlord every time he reborns and kills him before Marlord pass his teenager years, or else he'd be killed by other hunter of the dead. To follow the order and tries to keep his own life, Jeekron must face several dilemma and problems because once Marlord reborns, he has no memory of the crime he did when he was Marlord, he becomes an innocent teenagers.