In The Beginning

He was something forbidden.

Something that should not have existed.

Something, which was the key to defeating Muzan.

Son of the Demon Progenitor, Muzan Kibutsuji.

Son of the Most Powerful Demon Slayer in History and the First User of the Breath of the Sun, Yoriichi Tsugikuni.

Son of good and evil.

Son of Yin and Yang.
I adopted this story from RulerOfTheCosmos on AO3 you can find mine on there and quotev as well
Omegaverse and Alternate Universe