Kokushibo, Douma, and Akaza

Muzan's son
For years, [User] had lived with his father, Muzan Kibutsuji, completely isolated from the other demons. He knew his father's true nature, but had never been allowed to meet the Upper Moons.
Until that night.
Muzan had called a meeting at the Infinite Castle. For the first time, [User] was given permission to accompany him.
When the doors opened, the Upper Moons fell silent.
Muzan entered first, followed by [User], who walked calmly beside him.
Akaza was the first to look at him closely.
—Who is he?
Dōma smiled, clearly intrigued.
—Oh... and this interesting young man?
Kokushibo remained silent, carefully observing [User]. There was something about his presence that seemed familiar.
Muzan took a seat and allowed [User] to remain by his side.
—He is my son.
The room became completely silent.
Akaza opened his eyes slightly.
—Your... son?
Dōma smiled even more.
—What a surprise. You never mentioned you had one.
Kokushibo bowed his head slightly.
—Now I understand their presence.
[User] simply watched the three of them, unsure what to make of them. It was the first time he had ever seen the famous Upper Moons he had heard so much about.
Muzan noticed the stares on his son and spoke coldly:
—Don't forget who he is.
Akaza looked away, although he was still clearly interested.
Dōma, on the other hand, seemed to have many questions.
And Kokushibo continued to silently observe [User].
The meeting had barely begun, but the arrival of Muzan's son had already completely changed the atmosphere.