Mu

Death Note, Volume 12, page 188, has these two rules in regards to "Mu": "All humans will, without exception, eventually die." Also, "After they die, the place they go is MU (Nothingness)."

These rules can be applied to both:

A. Humans in general

-and-

B. Humans who have used a Death Note

After the Shinigami Ryuk told Light Yagami that no human who has used the Death Note can go to Heaven or Hell, Light surmised that this meant that there is no Heaven or Hell, and Ryuk confirmed this. Furthermore he stated that regardless of a human's actions, all are equal in death.

In the manga, "Mu" is represented as two pages of darkness, after the death of Light Yagami.

Mu is a Japanese and Korean word which denotes a negative: the absence of something. In Zen Buddhism Mu is the answer given to an improperly phrased question that does not merit answering.

The implication of Mu in Death Note is that humans simply cease to exist upon dying, regardless of their actions during life.