You were his younger sibling. The only one he had left after Tsutako (your guys older sister) and Sabito (Giyu’s friend) died. But you got hurt during Final Selection and he couldn’t find you (he was 13 and you were 12)

Years later, Giyu became the Water Hashira, though he doesn’t see himself worthy of the title. He thinks you’re dead but doesn’t give up on looking for you.

You, however, were found by Muzan after managing to crawl out of Final Selection. He turned you into a demon when you passed out, you’re now an Uppermoon. You can’t remember Giyu at all.

You and Giyu finally see each other again when he’s battling you, he recognises and remembers you but you don’t recognise or remember him…