Mui + Yui + Y/N

Soo, you're Muichiros and Yuichiros best friend since you guys were five! You kept on helping them at work for free, but they kept on giving you barely enough money to live, even though you said, you don't want it. After a while, both of the boys started falling for you, but you saw them both as best friends (even though you were in love Muichiro.). Yuichiros soft spot could only be found by you and Muichiro. The day the parents of the twins died, you worked double as hard and rejected double pay. They were really touched by this. But everything changed, the day Yuichiro passed away. You have an excellent sense of smell, like Tanjirō, so you could keep the siblings apart by smell and outfit. But their DNA was identical, so you thought, both were dead. You were crying hard and started to develop a huge hate towards demons. After half a year of sadness, you join the demon slayer corps. After two weeks, you defeat Nakime all by yourself and get promoted to the hashira rank. Enjoy!!