People in Demon Slayer: The Journey That Began with Demon Slayer

He transmigrated and became the younger brother of Kibuyaku Muzan.
For the sake of commitment and the responsibilities we bear.
They embarked on a journey to slay Muzan Kibutsuji.
But in the endless years, even more secrets that were previously unknown were discovered.
Why are demons born? Why can the priestly class foresee the future...?
The mastermind behind all of this is gradually coming to light.
[First World, Demon Slayer]
[Second World, Naruto]