Lilith's Seed

Lilith's Seed (悪の傷跡;Aku no kizuato, lit. Evil Scar) is a ability belonging to those who are descendants of the "Mother of All Monsters" and Wife of the Original Lucifer, Lilith. Talked about as a horror fairy tail to young devil children, Lilith's Seed is a unnatural power that activates as a vital organ inside those who are descendants of Lilith. So far the only known members who possess one are Rizevim, Lilia (Rizevim only daughter) and a unknown third person who gained one by devouring some of Lilia's skin when she was young with Yusei Satan-Lucifer and Vali Lucifer, having the potential to possess one. During the Great War this was the most feared ability being seen as a horror/freak show curse or unnatural mutation to the Descendant of Lilith. It was revealed that Lilith created a race of demons with Lilith's Seeds but Michael wiped the race out after the death of Lilith and the original Maous.

It is later revealed that Lilia is currently raising an army of humans who she is turning into Lilith's Seeds demons called "False Children of Lilith". Her plan is to purge the world of all other deities and buddhas using a army of Lilith's Seeds. Despite having the same plan as her father, she wants to kill him for what he did to her brothers (pitting them both against one another until they died).

Summary
Lilith's Seeds were the most feared power in the Underworld. Lilith's Seeds manifest as predatory organs and functions as a weapon and claws. It is usually as red as blood and flexible like the flow of water, but firm and sturdy. When released, the wielder's physique is strengthened, they are more resilient and their mobility heightens. Lilith's Seed can become as solid as teeth and can be described as "liquid muscles". The Lilith Seed's are released from the body piercing the skin, and the released blood form the Lilith's Seeds. The Lilith's seed can be repeatedly hardened and softened at will by the wielder. The Lilith's Seeds come in many forms with some being claws on the wielder's hands and others being

When in use the wielder's eyes will also become a strange green-bluish color and their pupils become more cat like and stretched out.

The reason the Lilith's Seeds are so feared is because if used too much they will cause the wielder to have to rely on eating flesh of other creatures in order to survive. It is even revealed that this is the reason Rizevim doesn't use it because he doesn't want to have to be delayed by such weakness. The wielder will also lose the ability to eat normal food, vomiting it up and eventually it can make them sick. The wielder also takes the risk of going insane if they are too emotional during a fight or during a traumatic event where they lose control of the seed and it overtakes their body.

Lilia, the descendant of Lilith and daughter of Rizevim is currently raising an army of Lilith's Seeds by using her unique power to turn humans into demons. So far all the members are shown to be all young children and teenagers with the oldest one she turned being younger than Rias.

The only case of a "Unnatural Lilith's Seed" is from a devil boy during the Great War the same age as Lilia who during a mission after almost dying, he ate one of Lilith's Demons, gaining their power of the Lilith's seed. So far he is seen as a criminal in the Underworld.

Forms
Standard Lilith's Seeds: The normal Lilith Seed of those who are the descendant of the Original Lilith, it acts as a predatory organ to the wielder.

Unnatural Lilith's Seed: The only abnormal case of a devil boy. By consuming one of Lilith's demon's he gained the ability of that Lilith's Seed demon.

False Children of Lilith: A faction created by Lilia where she is raising her own army of Lilith Seed wielders. They were all at one point normal humans that she turned into Lilith's Seeds by using the unnatural power she has which is the ability to turn other creatures into Demons by biting them and passing on the "Curse".

Trivia
This concept is based off of the Kagune from Tokyo Ghoul.

The mark is based off the curse marks of Orochimaru in Naruto.