Death Eraser

The Death Eraser is a plot device exclusive to the pilot manga.

Background and Mechanics
Feeling remorse after killing with the Death Note, Taro Kagami is offered the Death Eraser by Ryuk, and is told that he can erase the names in the Death Note and the victims will miraculously come back to life. He does so, and discovers the following day that the bullies that he had killed with the Death Note are revived.

The Death Eraser does not exist in any other Death Note media other than the pilot manga. In the main manga and animé, however, it is revealed that if a name or cause of death is struck out with two straight lines before the forty seconds has elapsed, then it can be changed or not happen at all. It is also revealed in chapter 107, that "Once a name is written down in the Death Note, There is nothing you can do about it."