Silent Killing

As the name suggests, this technique is simply a very quiet method of killing an opponent, usually from behind with a blade. Additionally, because the user is very silent, it cannot be defended against. The user will often slit their opponent's throat, preventing any cry that might give them away. The are said to be masters of this technique, and were even good enough to track and kill opponents through sound alone.

This technique can also be further enhanced by using the Hidden Mist Technique to hide any faint movements the opponent might be able to see.

Improvements
Gekihen can use this technique in unison with his Body Flicker Technique by silently and instantaneously appear with his blade in the targets throat with his right hand and his left hand holding the targets mouth, allowing a shinobi absolutely no chance to evade. He can also use it in conjunction with the Hiding in Mist Technique to increase its lethal capabilities.

Trivia

 * Although the name of this technique is written in kanji (無音殺人術), its pronounced in English ("silent killing"). The Japanese pronunciation of the kanji would be Muon Satsujin Jutsu, which would literally translate to "soundless murder technique".