What If My Fake Little Brother Is Muzan?

What should a viewer with the Will of Conquerors do after transmigrating into the Demon Slayer world? Ubuyashiki Yueying will honestly tell you: she has no idea she's transmigrated into an anime!

And nobody told her that the scumbag her friends called unforgivably vile was named Muzan Kibutsuji. Before becoming a demon, Muzan was Tsukihiko, a frail, sickly little patient who was easy to bully and push around!

As a good big sister, once you have a little brother, of course you have a servant you can legally boss around! Isn't it only natural to order him to do this and that? And isn't it perfectly normal to give him the occasional punch or kick?

All of that would be fine if her little brother weren't Muzan Kibutsuji, and if he were actually her biological brother.

If she'd known her little brother was the villainous boss, she would have treated him kindly and politely, then followed her boss and enjoyed the benefits. No, wait, that's the wrong way to think about it. A villager of Konoha with the Will of Conquerors would never act so spinelessly.

After years of making Muzan her slave, he now looks ready to kill her. He's probably going to slit her throat the moment he becomes a demon.

After discovering that she herself was adopted, and that her frail little brother was about to become a bloodthirsty, heartless demon, Ubuyashiki Yueying hurriedly married herself off to save her own life.

But on her wedding night, the person waiting for her wasn't her new husband. It was Muzan, his face deathly pale and his eyes bloodred.

"Heh, big sister. Where do you think you can hide?"

Oh, crap. She's dead.

Back when he was still Tsukihiko, Muzan had a woman he hated with all his heart: his big sister.

She had the healthy body he yearned for, and she showed him no respect at all. She made him run errands, make her bed, and, worst of all, do the laundry.

That woman was so wicked and outrageous. There was no doubt Muzan hated her.

Then, on the day he gained power, he came up with a way to take revenge. He would turn Yueying into a demon and let her experience what it was like to be a subordinate.

Of course, she would be his subordinate alone.

A universally adored female lead, probably with multiple endings.

Theme: Violence cannot solve every problem