An individual with the eye power of the god of death can tell the name and lifespan of other humans by looking at that person's face. By possessing the DEATH NOTE, an individual gains the ability to kill and stops being a victim. From this point, a person with the DEATH NOTE cannot see the lifespan of other DEATH NOTE owners, including him/herself. But, it is not really necessary for the individual to view the lifespan of him/herself nor other DEATH NOTE users.
