Demon Slayer

Demon Slayer (悪魔 スレイヤー Akuma Sureiyā) is the Quirk used by Sylvia. It is the result of an extremely rare mutation, and is said to bear no resemblance to any Quirk on either side of her family's lineage.

Description
Demon Slayer grants the user characteristics belonging to a demon.

In this form the physice of the user remains the same. Although they gain physical demonic traits.

In this form, the user's physical strenght is enhanced, allowing them to fight easily in close-combat. Their strength is enhanced to the point that a kick can sever heads and doors with ease, even leaving craters in the ground. Some user's strength is extremely high for a Demon who has never eaten a human, with their strength being able to match even that of an Upper Rank Nomu.

Rarely some users gain the ability to continuously restore power, without consuming any human life as it is the normal method for most demons. Instead, they recover strength through mere sleep.

As a subset of the above, users have shown to be able to grow stronger without any training or consuming humans. This ability is shown to trigger even in the midst of battle and with huge boosts. User's have shown to power up considerably as time passes.

User's have a strong regenerative ability, able to heal any sort of injury caused by a conventional mean in mere seconds. That includes regrowing limbs and organs.

Weaknesses
In this form, she is able to regenerate severed limbs, but any damage done before turning into this form can't be regenerated.

Due to her having the characteristics of a demon, she is not allowed to eat meat even when out of her demon form, since consuming blood would harness her bloodlust. Seafood seems to be an exeption as long as there is no blood, like octopus.

Usage
When using this quirk, Sylvia gains visibly large, prominent fangs, and sharp, claw-like nails that fade to red where they point. Her hair turns black, turning a flame-orange color as it passes her elbows, and appears to be crimped into large, straight ridges, worn side-swept drastically to her right. Her eyes turn a soft-looking, pale pink that appear a lighter color around the rims of their irises, slanted downwards towards the sides of her face and framed by notably long eyelashes, the pupils of which can appear slit as she transforms.

As a demon Sylvia has a strong regenerative ability more than any living being or human, able to heal any sort of injury caused by a conventional mean in mere seconds. Originally, Sylvia's regeneration abilities were a bit slow, healing faster when she slept, but her regeneration ability is enhanced when she fully transforms into a demon. The greatest evidence of this was during her battle against Shigaraki Tomura where her arm was blown by his attack, but after regenerating she was able to face him in an even match (by turning full demon), where she regenerated her severed limbs at the speed and proficiency as Shigaraki.

When Sylvia is in a dire situation, she can transform into a berserk-like state, with demon crests, that appear as vine tattoos, circle her body as well as a Demon Mark appearing over her left eye, her veins popping out, and her eyes turn fully black. This form enhances Sylvia's fighting ability, at the cost of her becoming more demon-like, including the need to feed on human blood.

Trivia

 * This is the other quirk belong to Sylvia, the other being Sky Dragon Slayer, using this one rarely to avoid accidental consumtion of blood.