The full name of the technique is as follows: The all-consuming Seal of the Dead Demon - a technique belonging to the sealing group was developed by the Uzumaki clan. The method is able to call to the performer Shinigami - the god in charge of death (which is why such an abbreviated name).
Start
The seal of the God of Death allows the shinobi to separate from their bodies and be suspended in their back. After this, a Shinigami arises behind the spirit, whose task is to bind a person’s soul with his hair. This process is visible only to both of them.
After the perfect actions, God wraps his left hand with prayer beads and reproduces strange and understandable lamentations only to him. The rites form a damned seal on his hand.
Main action
Then the God of Death launches this hand into the soul of the one who called him, so that he can invoke the Shinigami power to himself. After a successful contact, the Hand of Death emerges from the body of the shinobi and takes the soul of the enemy, which is already able to see him.
After capturing the spirit, the shinobi must seal it into his own body. However, this does not mean that the whole action takes place automatically. The contractor has to rely not only on technology from the outside, but also on his own strengths.
When the Seal of the God of Death is no longer valid, a sign will appear on the belly of the shinobi. After that, there are still a couple of minutes to complete the unfinished business to the end or to voice unspoken words.
Total
Further, the Shinigami begins to absorb the soul of the shinobi and those whom he sealed in himself earlier, which entails inevitable death. Eaten spirits are not able to get into a clean world until the damned seal is removed. Remaining in the stomach of the God of Death, they are doomed to eternal confrontation with their victims.
To avoid such a fate, there is only one option - apply the Shinigami mask by putting it on your face. Thus, a person is free to subjugate the power of the God of Death and make him rip open his own stomach, releasing sealed souls.
Using the equipment also entails physical injury. One side effect may be limb paralysis.
Application
The nine-tailed fox (Kyuubi) was sealed in exactly the same way with the help of the Fujutsu of the Four Symbols and the Seal of the God of Death in Naruto, who became jinchuuriki.
Hokage Minato sacrificed his life and the fate of his newborn son, having committed such a terrible act on him in order to save the people of the whole village of the Hidden Leaf.