Demon Slayer: The Butterfly's Secret Blade

This is a dual-protagonist story. Hudie Yuexiao is Shinobu Kocho's second older sister and Kanae Kocho's younger sister, while Fuqiu Yiguang is Giyu Tomioka's younger brother. The two protagonists work hard together and become Hashira before long. In the end, they defeat Muzan at the Infinity Castle. (Note: Hudie Yuexiao and Fuqiu Yiguang are a couple.)