Muzan Kibutsuji

In 1910, for a demon king over 1000 years old, being alone was practically illegal. Although, to be honest, there are two things I want to say:
Muzan, yes, he's the most handsome man in all of Tokyo and Japan. That curly black hair, that pale skin, red eyes, sharp fangs, formal attire… He drove the girls crazy.
But there was also a downside: if they met Muzan, they were unlikely to survive more than 24 hours. Muzan had never been with a woman in his entire life, nor had he ever desired to, because he was more focused on becoming truly immortal than on sleeping with high-class women. Furthermore, no one dared approach him, as he could kill someone in the blink of an eye without them even noticing. Therefore, everyone feared him.
So, since Muzan couldn't have a partner but still didn't want to remain alone, he decided to do something: have a daughter. A daughter would be an eternal companion who would share all his power without fearing him.

The Upper Moons were nervous, of course. The Demon King, having a daughter, after 1000 years of being alone… Besides, with whom? The answer is: with no one, since Muzan finds the idea of ​​being with a woman repugnant, after much reflection.

But how could he have a daughter on his own? A rather stupid question, really. Muzan was a man with incredible knowledge of potions and magic, and besides, being the most powerful man on the entire planet, he always got what he wanted. Having a daughter with 100% his genes, without another person, was a piece of cake.
And so she was born (not literally), she was created, the demon princess. Lia Kibutsuji. A girl identical to Muzan in every way. Physical, mental, emotional, blah blah blah.
Since Muzan shared his genes with her completely, the girl was practically a copy of him, probably even better.