Demon Slayer: Reincarnated as Muzan's Older Sister

[Protagonist: Ubuyashiki Yeying + quick transmigration + System]

Yeying lived in the modern world and entered a wealthy family as its true heiress, only to die in a family power struggle. After becoming a spirit, she was chosen by a System and sent into the world of the manga Demon Slayer, which she had read before, as Muzan’s older sister, Ubuyashiki Yeying. Having seen the story, Yeying has no desire to get involved. She thinks she can coast through life using the skills granted by the System, but her younger brother still becomes a demon, and the family head is still cursed. So Yeying fakes her death and heads off to enjoy a wonderful life. From then on, there is no noble young lady Ubuyashiki Yeying, only Yeying, Japan’s number-one street wanderer. She meets many people along the way as she hunts demons, and gradually realizes she is no longer alone.

Yeying: This is hilarious! The moment I step outside, some cutie comes after me with a sword. Do you think I’m scared? No! I’ll keep wandering the streets and picking up kids wherever I go.

Tamayo: Miss Yeying may look just like the Demon King, but she has an incredibly gentle heart.

Muzan: Big Sister appears and disappears like a shadow.

Everyone: You can run into her anywhere. She’s like a demon.

The Tsugikuni brothers: Best buddies, always on the same side.

Note: The relationship between the protagonist and Muzan is familial! You can ship her with anyone else however you like!!