Demon Slayer: After Becoming Muzan's Sister, I Tear Fate to Shreds

[Mutual healing] Two female leads (their relationship can be familial or romantic, whichever you prefer) + split personality + Demon King + strong female lead + no CP + psychological healing + medium-length novel + no breaking up any canon couples [I'll try to keep everyone in character]

Multiple twists in the middle. (Kaigaku has a storyline.) This isn't a traditional power fantasy! (The story includes fourth-wall-breaking scenes and direct interactions with readers, starting around the middle, at roughly 50,000 words.)

Jian is the eldest daughter of the Ubuyashiki family. After finally managing to die of old age, she was just about to ascend to heaven when her infuriating mother saddled her with the mission of saving Japan.

[Did you even ask me first? Hey?!]

She wakes up one day to discover that her hallucination has become a soul living inside her body!

[Who could possibly accept that?]

Jian and Lianyue, the soul with whom she shares her body, form a bond and work together to protect each other as they navigate the conflict between Muzan and the Demon Slayer Corps. Deals, battles, and buried secrets intertwine. When Lianyue faces the threat of disappearing, a thousand-year journey of protection and redemption begins.

Due to health issues, I had to wrap things up hastily, but it does have a happy ending. The story is just on the short side, with few transitional scenes, so the pacing gets very fast toward the end. Please be kind!