This technique Ura Shishou is a fūinjutsu utilized by Danzou. The fūinjutsu can be placed on the user's chest and others as well with specific seals. This technique acted as Danzou's final technique and was set to activate upon his death; when used the technique releases four symbols from the user's body and forms a large black sphere around them. Anything within the sphere of activation would be sucked away into the body and sealed away permanently.
The name and appearance of this technique are a reference to the Chinese "Four Symbols", known as 'Si Xiang', which are produced from yin and yang, and act on the ba gua. These symbols are named: 'lesser yin', 'great yin', 'lesser yang' and 'great yang'.