Power of Souls

"The true power of the Alastor Clan, the ability to manipulate one's very soul and the souls of others."

- Gray Dantalion explaining Soul Eaters Power of Souls also known as "The Power of Souls", "Crown of the Mad Devil King", "Thesis of the Mad King", and "King Slayer Technique" is a very powerful devil clan ability belonging to the Alastor Clan. First used in the Prologue when Ichiro Alastor uses it during the fight with Raynare and a pack of stray exorcists, it is a ability that allows one to manipulate their very soul or in the case of the Original Alastor, to manipulate the souls of others for combat.

A dangerous ability created by the Original Alastor due to his manipulation and experimentation with the souls of other beings. It was believed to have been lost after the civil war when Seth Alastor died by the hands of Rizevim until it was revealed that Ichiro Alastor was alive.

Summary/History
The Original Alastor was a devil who worked alongside the Four Original Great Satans. He would experiment on souls even conducting experiments on his own soul and the soul of his own son. The original Alastor also consumed souls of fallen angels and other beings he killed during the Great War. The original Alastor also had his whole harem who even the goddess Aphrodite was a part of. Alastor was able to turn some of them into Soul Eaters by having them consume his blood.

Eventually the Bael family found out about this and not wanting this technique to spread throughout the Underworld because of the danger it would cause enlisted the help of the Raim Clan King, Seere clan Queen, and Andras clan King in order to kill Alastor. Alastor using his harem members that became Soul Eaters slaughtered all three of them and their families which is why this form of combat was named "King Slayer Technique" because using it he was able to kill three devil Kings/Queen and kill their families thus aiding in the families extinctions. It was then Zekram Bael himself, using a army of high class devils killed the Original Alastor and his harem members who had become Soul Eaters sparring the young son of Alastor, Seth Alastor.

Seth Alastor was a young devil who fought alongside Sirzechs Gremory and Ajuka Astaroth during the conclusion of the Great War. A unknown young devil with great power who became friends with the two during the Great War because he was such a aid in a time of distress and he had Zekram Bael backing him up nobody questioned his appearance or his origin. Sirzechs and Ajuka while fighting alongside him realized he possessed a very unnatural ability, the ability to eat the souls of the angels, fallen angels, and other beings he would kill. Not understanding the nature of the ability themselves, they decided to keep it hidden.

After the conclusion of the Great War, when the Original Great Satans were killed, Sirzechs and Ajuka both became devil kings and Seth Alastor was given his own evil piece set. When the Civil War between the Old Satan Faction and New Satan Faction began, Rizevim Lucifer, asked Seth Alastor to join the Old Satan Faction but Seth Alastor refused and tried to kill Rizevim only for him to beat Seth to near death. When Seth woke up, he realized that Rizevim slaughtered his entire peerage.

In anger, he vowed to kill Rizevim joining the New Faction Satan. It was then he met Camilla Mordred, a outcast from the Pendragon Family because she was related to the traitorous night Mordred Pendragon. The two eventually got married and had a son. Later, the two were killed by Rizevim which is revealed to Ichiro in Life 1.

Ichiro as their son in Life 1 and he inherited the Soul Eater power from his father. Sirzechs and Ajuka don't outright ban the Soul Eater's abilities but make it illegal for Ichiro Alastor to consume souls to increase his power.

Powers and Abilities
Soul Eaters are powerful abilities because they allow the Alastors to use their own souls in order to preform powerful demonic abilities. The Original Alastor however possessed the ability to use the souls of others in a way that didn't require eating their souls.

66 Abilities of the Mad King (マッドキングの能力; Maddokingu no nōryoku) The Original Alastor had created 66 different abilities out of the Power of Soul. But they are believed to be lost in history with only 5 of these abilities being shown in Ichiro.

Soul Flames (魂の炎; Tamashī no honō) also known as "Fire of the Devil's Soul" is a very powerful ability originating with the Original Alastor that allows a member of the Alastor Clan to create demonic flames by using their demonic souls as a basis. These flames being made of their own demonic soul is very fatal to creatures that are holy in nature like angels and fallen angels. The flames are always a dark color, with Ichiro's being dark purple and black and his father's flames being dark blue. The flames is a representation of the color of their demonic souls. The flames are said to be able to go on par with even the Phenex Family and Dragon flames.

Dark Creation (暗い創造; Kurai sōzō0 also known as "Demonic Birth" is a ability that allows a member of the Alastor Clan to create monsters and animals out of their demonic souls. They are however limited because the monsters are made out of their very soul it uses most of their demonic strength and energy just to make a few. When the monster dies however, the portion of their soul and energy used to make the demon goes back to them. Soul Summon also known as "Lost Trick of Creation" is a ability that allows a Alastor to create weapons out of their own souls. The Original Alastor and Ichiro possessed the ability to create spear(s) out of their souls while Seth possessed the ability to create swords. This Original Alastor was able to use the souls of others to create different weapons.
 * The Original Alastor according to Zekram Bael was able to create monsters on par to Annihilation Maker.
 * Ichiro is shown to be able to create goblins and hounds out of his soul.

Impurification (浄化; Jōka) also known as "Soul Corruption" is a ability that allows a Alastor to transfer their power temporarily to someone else. It is temporary and relies on tapping into the other person's soul and infusing their power with theirs. When a Alastor uses this, their soul and their abilities are cut in half.

Soul Eating (魂を食べる; Tamashī o taberu) a banned practice that allows a Alastor to consume the souls of other creatures souls to increase their power. Because the Original Alastor consumed the souls of fallen angels, he gained the power to manipulate light to a extent.

Special Moves
Dragon of Annihilation  also known as "Roar of the Mad Flames" is a powerful attack that relies on combining soul flames with dark creation to create a very powerful Dragon made of black and purple flames. This attack is shown to be very dangerous as it caused Ichiro's heart to temporarily stop and knocked him out, and severely burned his arms making it a very dangerous attack with Sona telling him to "only use it during emergencies", it is revealed that Ichiro learned this attack from the Demon Surgeon Shigure.

Drawbacks
Because the power relies on using the wielder's soul it can be very dangerous as they run the risk of consuming or even shattering their soul which could cause them to fade from existence. This ability also consumes a lot of demonic energy making it impossible for the wielder to use all these abilities at the same time.

Trivia

 * Don't confuse this with Houki Minami's Alastor Family.
 * The ability is based off of Soul Eater and the image used is Evan Soul from the Soul Eater series.