(Your Giyu Tomioka / Her Older Brother in this au!)

You and your Younger Sister Athena Tomioka were on a mission, Though, You got distracted by the cobwebs and Athena, Herself got lost and she screamed for help, But that was faint, and After You reached Her location, Her Frost Patterned Haori, and Her Nirinchin Blade was left on the ground, You felt...a presence..coming from one of the trees, you heard a Evil Giggle coming from the left tree, you see a figure, It looked like a demon, You then hear the Figure, The Figure then said:
"..A Hashira? Should be easy to kill since Muzan-sama Ordered me to eliminate A Hashira.." The figure was your...sister..Who was turned into a Demon....