Original Fandom: Demon Slayer
Demon Tanjiro and Nezuko come from an AU where the axe he threw wounded Giyuu and/or killed him, Tanjiro grabbed Nezuko and ran after and it took awhile for Nezuko to be more passive around him. He eventually allowed a demon to turn him and he dedicated his life to protecting the last bit of family he had. The two siblings eventually became immune to the sunlight and Muzan tried eating them to become immune himself. The two siblings overpowered the demon king and as revenge for killing their mom and little siblings... ate him.
Infected She-ra saved Nezuko from being decapitated by a Demon Slayer and Tanjiro was grateful, so grateful he pledged his loyalty to her and the two joined her team.
Demon King Tanjiro's Powers
*Almost Absolute Regeneration (By assimilating the blood of the Demon King, a being who possesses the fastest and most powerful regenerative power of all demons, Tanjiro's regenerative abilities surpassed those of all other Demons in existence, even Giyu Tomioka noted that this ability, along with his immunity to sunlight, makes him practically invincible to all forms of physical damage)
*Resistance to sunlight (After transforming for the first time, Tanjiro is initially affected by sunlight as any normal demon would be, however, he quickly develops resistance and is soon able to move in broad daylight without taking any damage , it is possible that he is able to do this because, as Muzan noted shortly before his death, Tanjiro is of the same blood as Nezuko Kamado who also overcame his weakness to sunlight as a demon due to his resistance to sunlight, all Nichirin weapons and even Crimson red blades lose their effectiveness, Giyu Tomioka stated that with his immunity to the sun, along with his enhanced regeneration, Tanjiro is practically invincible)
*Biological Absorption (Demon King Tanjiro has the ability to absorb, assimilate, and dissolve organic and inorganic objects)
*Transformative Blood (Demon King Tanjiro's blood has special mutagenic properties that can transform humans into creatures known as Demons, his special blood also appears to give rise to a multitude of Special Abilities to those who receive his blood, such as powerful and rapid regeneration, the power to control flesh, immortality, an accelerated growth rate, enhanced physical dexterity, and even supernatural abilities called Blood Arts/Kekkijutsu)
*Blood Memory Transfer (Demon King Tanjiro can pass his memories and memories to the Demons under his control, just like Muzan Kibutsuji himself did to him)
*Accelerated Development (Instinctively used some of Muzan's blood techniques, and Demon King Tanjiro would eventually regain his reasoning ability (along with Muzan's influence), especially if he satisfied his hunger after devouring a human)
*Biokinesis (As Demon King Tanjiro assimilated Muzan's blood, he subsequently gained his Blood Demon Art, which allows him to control various properties and aspects of his body, Demon King Tanjiro first displays this by projecting whips and appendages shaped like bone on his back, which he uses to extend his attack range, however, due to his savage state, Tanjiro has not demonstrated the same skill in wielding them as Muzan, but after regaining his reasoning ability he becomes better than Muzan, like Muzan, can create any antidote for any type of poison and can alter his physical appearance to look identical to anyone)