The Shadow Pillar

I don't own Demon Slayer or RWBY.

Blake Belladonna, in "The Final Word", she was dropped into the void under the Central Location by Cinder Fall, while trying to save Ruby from the same fate. Her current status is unknown. But that void actually lead to another world. Another dimension, filled with demons crawling everywhere in the night. She tried for 5 years to get back home, but nothing succeed. She lost faith that should would go home and learned to live with that fact she was never going home. Soon finding a Faunus Village filled with others like her, who were stuck in this world. Faunus were known for being demons for their animal like features and instincts in this world, but she didn't care. She had something close to home. And that was good enough for her. She fell in love, she got married, and she had a son. After 7 years of living in peace. Her village was attacked by Demon Slayers. Slaughtering the whole village to the ground, only her toddler, her a few others escaping thanks to the help of neighboring villages. But after two years off being on the run, she died while protecting her child. Her last words to him, driving him to the person who he is today. The second most powerful pillar, Kaigaku, The Shadow Pillar.

Also forgot to mention that everybody is in a different dimension. All them fell into different dimensions.