A Kamado got reincarnated into MHA (My hero academia FF) [Discontinued]

The new beginning after the end

GENERAL POV

Muzan injects Asahi Kamado with all of his blood, turning him into a demon.

This is the birth of the strongest Demon ever. Since he was the brother of Nezuko Kamado who was the first Demon to develop an immunity to sunlight and is capable of using the Breath Style of Yoriichi Tsugikuni, Thunder-breathing, water-breathing and wind breathing. As he slowly disintegrates, Muzan tells Asahi to make his dream come true and destroy the Demon Slayer Corps in his place. Unknown to Muzan, his dream will never come true.

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As Giyu Tomioka and Tanjirou kneels in front of Asahi, the surrounding Kakushi shed tears, one of them suddenly gapes in shock as the tumour from Asahi's head disappears and he opens his eyes to reveal a demonic gaze. To everyone's shock Asahi regenerates his left arm and swipes at the Kakushi next to him but Giyu and Tanjirou reacts quickly and pushes the Kakushi out of harm's way.

The other Kakushi look on in fear and ask Asahi why he is acting in such a manner, as the boy stands drooling profusely, enjoying his newfound fangs and claws. His Demon Slayer Mark mutates and grows down to move past the bridge of his nose, with another identical mark growing upwards from his neck to almost meet the other, similar to Kokushibo's Mark.

"Nii-san?" the shocked Tanjirou muttered as tears rolls down his face.

Giyu rushes forward, grabbed the stunned Tanjirou and yells at the other Kakushi to get away from Asahi as the boy looks to swipe at him. Suddenly, the sun shines brightly from the sky and Asahi double takes to look at it. 

He begins to burn and writhes on the ground, with his swipe at the Kakushi going off target but still managing to rip off the lower half of his mask. As Giyu gets in front of the Kakushi, he tells him to run away as he prepares to face this new threat, yelling for anyone who was still conscious to grab a weapon and begin fighting.

(A/N: Asahi is Tanjirou Twin Brother, He left the house to train as a demon slayer at the age of 9 with the permission from his parents while Tanjirou goes to sell charcoal. Asahi is born with a Demon Slayer Mark but he can't use Transparent World.)