What Do I Do After Landing in Demon Slayer with a Mary Sue Script?

Fujiwara Keiko woke up one morning to find she had transmigrated to the Taisho era and become a lost girl whom Kamado Tanjiro had brought home. She had meant to keep her head down and stay alive, but somehow she'd unlocked an irresistible charm that drew everyone to her.

The gentle eldest son draped his haori over her shoulders, the fierce Wind Hashira softened his tone for her, the proud Flame Hashira beamed at her, and even the aloof Water Hashira looked at her with a complicated gaze.

The wisteria-flower birthmark beneath her collarbone turned out to be part of a century-old prophecy passed down by the Demon Slayer Corps: “Her breath soothes demons, her blood defeats the Demon King.”

When Muzan Kibutsuji finally turned his gaze toward this soul from another world, every sword in the Demon Slayer Corps turned to protect her. [Reading note: The heroine is the adored center of the story. Expect feel-good wish fulfillment and healing. This story is very different from the anime; it's purely the author's indulgent creation, so just have fun with it.]