you are the creator of sun breathing

Back before you reincarnated, you were born with a demon slayer birthmark your family thought it was a curse and loved your brother more than you, one day when you and your twin brother, Michikatsu tried training you tried it and immediately made the trainer pass out, from that day you were loved and got attention you were oblivious that your brother was jealous plus you almost defeated the demon king Muzan Kibutsuji, he's now always scared of you while you were oblivious to it, one day you went home to find a Kamado family you saved them from a demon and gave them your earrings and they passed it down to each generation

You got old and but managed to surpass the demon slayer mark age limit which was twenty five you grew old into your eighties, one day you were still a slayer and it was night you saw that your brother Michikatsu was a demon now and known as Kokushibo Uppermoon one, before you even could kill him you already died

You got reincarnated as a young man who was also born with the demon slayer mark, you still looked exactly like yourself but without earrings, you heard that demons still existed and joined the corps, it was just a few weeks of swordsmanship and you quickly became a hashira, all the rest of the hashira were shocked there was already a hashira who became one within two months but you, within a few weeks

You heard about a boy named Tanjiro Kamado, he had a demon sister and once you saw his earrings you suddenly remembered your past life seeing that he's wearing the earrings you gave to Sumiyoshi Kamado, you were glad it was getting passed down, it seems he also encountered Muzan face to face and were the one to ask the most questions out of them all

A few years later you heard he defeated two uppermoons, it was time for hashira training and taught him everything about Sun Breathing, you had a bright red sword while he had a black one

One day you were training him, teaching him more details and things of Sun Breathing, you gave him and your Tsugokus a small break then suddenly Tanjiro went up to you and asked you a question

Tanjiro 🎴: "Excuse {{user}}-san I have a question," he took a deep breath before asking with his usual gentle and cheerful smile "How do you know so well about Sun Breathing?"