Demon Slayer Mark

The Demon Slayer Mark is mysterious marking that can be unlocked and may appear on the forehead or face of a strong Demon Slayer. It resembles the Demon Crests that Demons possess. It looks somewhat like a tattoo, scar or birthmark and each Demon Slayer Mark looks unique related to the Breath Style of the User. However the precondition in unlocking it, is that a individual directly related to the Breath of the Sun has been born with it, which will then spread to other strong Demon Slayers through resonance.

History
The true origin of the Demon Slayer Mark is unknown. However it is known that the first person with a Demon Slayer Mark was none other than the First Breath user. He was already born with it and it enabled him as a child to gaze through the "see through world" allowing him to see the disease of his mother, but also to defeat strong opponents by seeing their blood flow, muscle and joint movement. It is said that the Demon Slayer Mark has resonated then and have been awakened by other Demon Slayers, which would later lay the foundation for the Demon Slaying Corps and almost achieved killing Muzan Kibutsuji. The story of Demon Slayer Marks than has dissappeared for a long time due the fact that they have not been awakened by any other Demon Slayer after that, till the point that they have been rediscovered by Tanjiro and the current Pillars.

Unlocking
The Demon Slayer Mark can only appear in other Demon Slayers, if a individual directly related to the Breath of the Sun has underwent progress in his Breath Style and is near them. It is unknown how Breath of the Sun users or individuals related to it, have achieved it, but it is known that they carry it since birth.

Strong Demon Pillars near such Demon Slayer Mark born individuals may resonate and awaken the ability to get one for themself. Their heart rate will drastically increase alongide their body temperature, and if they survive the Demon Slayer Mark will appear. Each one of them looking unique and related to their breath.

Abilities
Enhanced Physical Capabilities: Before the unlocking of the Demon Slayer Mark, the user will feel a increased heart rate of 200 bpm and a increased body temperature going over 39° Celsius. If he survives this life threatening state, does his body adjusting to it and start to breaking its limits, granting the user superhuman strength, speed and enhanced breathing techniques beyond a normal Breath Style user. In this point their strength and speed even rivals that of stronger Demons like the Upper Moons of the Twelve Demon Moons.

See-Through World (きる Sukitōru Sekai?): A ability that enables the user to see the muscles, blood flow, and joint movement of living beings, allowing them either to accurately predict and react to movements or confirm their well-being (Gyomei and Kokushibo could confirm the death of Genya and Muichiro). Additionally does the user perceive fast movements as slow movements.

Crimson Red Nichirin Blade: Demon Slayer Marks may enable the users to dye their Nichirin Blade in a crimson red colour, giving their blades the properties of sunlight. Their blades then can incinerate Demon Cells and hamper Demon-Enhanced Regeneration.

Curse of the Mark
Having the Demon Slayer Mark has it's costs. Demon Slayers who have awakened the Demon Slayer Mark are said to die after they reached the age of 25 and Demon Slayers who have awakened the Demon Slayer Mark past the age of 25 will also die shortly after that. However their are ways to avoid dying through the curse shown by Yoriichi and Kokushibo. Through unknown means was Yoriichi able to defy fate and lived up to 85 years, while Kokushibo choose Immortality through Demonification by Muzan's blood.

Known Users and their pattern

 * Yoriichi Tsugikuni, with a flame like pattern on the left side of his forehead.


 * Kokushibo, with a flame like pattern on the right side of his lower cheek and one on the left side of his forehead.
 * Tanjuro Kamado, with a scar looking like birthmark on the left side of his forehead.
 * Tanjiro Kamado, with a scar looking like birthmark on his left side of his forehead like his father at the beginning. After getting injured in the Final Selection does it start looking like a big scratch growing later further into a flame like pattern resembling much the design of Yoriichi and Kokushibo.
 * Muichiro Tokito, with a mist cloud pattern on both sides of his cheeks and one on the left side of his forehead.
 * Mitsuri Kanroji, with a double heart pattern above her clavivle on the left side.
 * Giyu Tomioka, with a water stream like pattern on the left side of his cheek.
 * Gyomei Himejima, with a pattern on both his forearms resembling breaking rock.
 * Sanemi Shinazugawa, with a windmill resembling pattern on the right side of his cheek.