The Six Demons in One God Style is a deadly swordsmanship martial arts that extremely, if not solely, emphasizes on offense. Rivaling Pray Style in power and difficulty, the Six Demons in One God Style possesses utterly destructive and fatal techniques but practicing them would also overburden the user to the point that it would deteriorate his/her health. Sometimes, the user may even end up taking more damage than the opponent - if not die from outright practicing it. The final and most potent technique in this style would require the user to sacrifice his/her own life in exchange for overwhelming strength, akin to pure invincibility, that can overcome any and every obstacle but only for a brief duration.
The Six Demons in One God Style is notoriously lethal for both the user and the target of its techniques. Only those with paranormal powers such as fast regeneration, resurrection, curser abilities, or other powers that can circumvent its side effects can survive using the style with little to no negative penalties. As such, practicing this style seems to be an unspoken taboo among Knights and other martial artists.
Whereas Pray Style is the self-realization of victory, the Six Demons in One God Style is the manifestation of sacrifice, risk, and desperation. The style provides skills that surpass one's own talents and power at the cost of a shorter lifespan.
The "Six Demons" on the style's name reflects its six main fundamental points - referred to as evil acts - that are the basic stances forming the different techniques and special attacks under the style:
- First Demon - a stance that increases the movement of a user and accelerates succeeding strikes while simultaneously enhancing reflex as well. In effect, it appears as if the user made a high-speed, dashing attack. It also seemingly enables the user to make countless strike in a single moment. The First Demon is best used as a counter and parry form as it can make a contraflow strike directly opposite to an incoming one.
- Second Demon - a stance that concentrates and compresses black miasma in order to create a force projection. Releasing the stored miasma results in a violent miasma wave that propagates in a linear direction which slices everything it passes through. The Second Demon provides users diverse techniques to extend their range.
- Third Demon - a spinning stance that allows the user to create rotary strike techniques. Users create an endless torrent that maximizes the damage potential of their strike due to the scaling momentum of their spin. The Third Demon can cut down anything within its area of effect or range.
- Fourth Demon - an unusual "reverse-Iaijutsu" stance that stores black miasma and then releases it on a desired target - effectively striking from a distance without movement. The exact theory and process of the Fourth Demon are shrouded in mystery. Users are able to perform techniques with the Fourth Demon by unsheathing their sword halfway or at least a quarter from the handle (storing action), and then quickly sheathing back the revealed portion of the blade (releasing action). Practicing the Fourth Demon is too dangerous due to its excessive recoil damage. Additionally, it may be too unstable or inaccurate to be effectively used - in which case the user would definitely end up with worse injuries than the opponent unless a lucky, critical hit is made.
- Fifth Demon - a stance that sets a user for thrusting techniques. The Fifth Demon allows the user to move and strike rapidly with each strike imbued with force projection to deal explosive damage. Users can also manipulate black miasma by first charging it then releasing it along with a thrust. In this form, the miasma acts as a straight, needle-like beam that can pierce through any material and also extend the user's range.
- Sixth Demon - a buffing stance that grants temporary invincibility to the user by converting his/her body into a battle-oriented living weapon for a limited duration which seems to be dependent on the willpower of the user. In this transformation, all of the user's biological organs are adapted or streamlined for combat use. The Sixth Demon is an immediate level-up that enables a user to be at par with the Knight Order's Top Sword and/or the Beasts' EX-Type Zeroes. When activated, a simple swipe of the hand is elevated to a destructive-scale. Moreover, the user can also perform powered-up versions of this style's techniques while the Sixth Demon is active. The Sixth Demon is a forbidden technique since it results in immediate death after the status expires.
Using the Six Demons in One God Style produces a unique mist-like black miasma that reflects the power of its techniques. The miasma itself is neither a paranormal power nor a wave but a mysterious part of the style. It surrounds the user and also follows the strikes made with the style's technique. When the Sixth Demon has been activated, the user's heart is consumed by the miasma and transformed into a black core; the miasma then envelopes the user. It is unknown whether the miasma actually applies the damage (i.e. the strike itself) or simply marks the target and other hit areas. Furthermore, it has unknown qualities that grant flight, wave/particle beam-like force projection, and barrier-like shielding.
Ray Nelson attempted to analyze the Six Demons in One God Style during his fight against Van Nelson. He observed that the black miasma being manipulated for the techniques under the Second Demon are "gravity elements".
The following are certain variants of the Six Demons in One God Style that were shown in the Knight Run series:
- Imitated version - this variant is a diluted version of the original that only imitates it so that the negative side effects to the user would also be proportionally weaker. Thus, this variant makes it possible to practice a weakened Six Demons in One God Style for those without the necessary powers and abilities to negate the style's inherent danger. However, the recoil damage still remains considerable and life-threatening. Leny taught Van Nelson this imitated version to make him stronger and he continues to practice it with reservations.
- Steel Art of Evil - Van used the imitated version to withstand and control his newfound magnetic abilities acquired from Ray Nelson. This variant combines the activation of the Six Demons in One God with the techniques of the God of Metal.
- Queen of Catastrophe - a series of rapid slashes aimed at cutting off extremities.
- Hideous Serpent - a technique that requires the user to bend the blade of a sword to an abnormal degree before releasing it. The force of the blade springing back to its original shape is magnified such that it produces a linear force projection used to strike targets at a distance.
- Inside the Hideous Serpent - Two Evil Serpents - creates two intersecting force projections that forms a slicing X-line. The technique is done from a single Hideous Serpent movement but the fingers are also spun as they bend the sword.
- Ear - a low strike aimed at the knees and below.
- Return of the Sky from Evil Grounds - Three Streams, Red Wind - a series of spinning attacks that coalesce to form a tornado-like torrent around the user.
- Rakshasha - an unforeseeable strike that cannot be parried or evaded; its only weakness is its lack of stability and accuracy in target acquisition.
- Demon Line - a charged-up piercing thrust. Once the thrust is made, it does a secondary, larger damage by releasing pent up black miasma to create a delayed explosion.
- Line of Disorder - a series of quick thrusting strikes thrown one after the other.
- Barrier creation - black miasma forms a spherical envelope that negates incoming attacks.
- Leny - Master of the Six Demons in One God Style; Leny is able to practice the style without suffering from its consequences due to her Curser ability which passes the recoil damage she is supposed to receive to a different person.
- Van Nelson - Leny's disciple; Van uses a diluted form of the style (closer to being an imitation) since he cannot endure the original, full version. His practice of the style is compromised due to his deliberate refrain from using its monstrous power as well as his reluctance to kill. Inadvertently, Van also innovated the style from his imitated version so that he can use it in conjunction with other styles and abilities. He was able to greatly enhance the use of this style's techniques using AB Sword Number 30. Arondight's Masterpiece.