Devil Release

is an immensely destructive energy composed of an individual's very own soul, corrupted beyond repair and entirely embraced. One cannot access this form of energy unless they meet the conditions to first use their own life force. It is unknown just how many individuals can do it in the world, but the most notable user in the realm is the Demon of Chaos.

Gaining the Power
One's soul is composed of two separate energies (much like chakra), Good and Bad, or Positive and Negative. Normally, those two energies are fairly balanced, only leaning a tad in an individual's chosen alignment (let's say by 10%). Of course, with each deed, it's inching ever closer and closer towards that specific alignment choice. The further one goes towards that particular direction, the easier it is for that person to continue doing whatever it is that they're doing. Whether they're:

Or
 * Good people, more inclined to help others
 * Evil people, more inclined to help themselves.

The first step to reaching the power of one's soul is very, very, risky as you would need to nearly deplete your chakra reserves. It's not only the act of being nearly completed, but your very being would need to be in such a stressful and completely desperate state of exhaustion. When the body has reached such a state, with no energy to cling onto, it'll be forced to break through its own limiter to grasp at the body's last stores of energy, the soul.

For one not to die during this time, they would need to have a very powerful body beforehand, one capable of taking vast amounts of damage, and a stronger willpower, with such power to beat death away and hold onto the living world. Because of the dangers present in getting too close to such a condition, most resort to popping a Soldier Pill before they could get close. If they were to neglect their body's screams of pain and continue with their fight, they would find themselves invigorated by the purest form of life energy. This energy would automatically (and quite frantically) heal the body just enough to remain alive.

Individuals with power life force like the Uzumaki Clan and Senju Clan will gain more health upon breaking their limiter. Those of lesser standings will lose a considerable amount of their life force and their natural lifespan will forever be shortened.

Corrupting that Power
Even when one is on the very edge of the Evil spectrum (99%), their soul could still be saved and they have a chance of returning balance. But if one is truly evil they can denounce their humanity and entirely embrace the evils of the world, effectively weaponizing their soul. Of course, once denounced, the individual cannot ever return balance to their soul and can never truly learn to genuinely feel compassion, their Sins growing stronger and completely taking control of them. Also achieving this form can eventually mutilate the human body, especially if it's full potential was ever used.

Various forms of corrupting energies, like Dark Release and Blood Release, can quicken this process and make the journey all the more fulfilling in the end. Of course, without a pact with an evil deity like Amatsu Mikaboshi, the God of Chaos and Darkness, one can't possibly continue to use this power without further damaging their soul and shortening their natural lifespan.

With the pact, not only can their soul be repaired, but they can also add onto it with souls of those they manage to kill. The stronger the person, the stronger the boost of power. Of course, with the more souls, the stronger the corrupted soul gets and the more dangerous it is for both user and target. Other deities with power over souls, even Amatsu Mikaboshi, can lay claim to the wares and immensely damage the host and severely hamper their overall progress. So staying on the good side of a deity's generosity is a plus, especially since said deity can mutilate the user's very soul and turn them into demons.. or devils, hence the name. Doing this and their body is then able to withstand the full potential of Devil Release.

Usage
Devil Release can be used just like any source of energy at a user's disposal. At it's purest form, it can be used to augment attacks or even regular techniques much like Sage Mode. Of course, it can be used in it's own set of techniques and if its used in such a fashion, it has the uncanny ability of causing severe damage to the target's soul. In time, the soul can be repaired, but it'll take a very long time for that to eventually happen.

An example of this specific usage of power is the use of the Sins of Corruption, a group of spirits derived from the Seven Deadly Sins (More on them in the link).

Through Devil Release, if one hadn't already possessed a healing factor, they can either develop one of considerable efficiency or cause the already existing factor to increase exponentially. Because, despite losing the Positive side, the soul still has that ability to heal.