Omega Sigma

Omega Sigma is a technique created by Sigma Uchiha, after opening the Fourth Gate of Pain — and unleashing a immense force of pressure.

Usage
Sigma will begin to form a unique hand seals, which represents the kanji "Sigma" — also being his name. Once down, Sigma will create what his known as the "Sigma" hand seal, by pulling all the way back, and pushing forwards, Sigma pushes out a force of energy around himself, in the shape of "Σ", which will begin to tear the opponents inside muscles and tissue apart.

Countering
The shape the technique takes on is the kanji; "Σ" - as you ca see there are three open points. If the foe manages to slip through one of the points, they take little to no damage.