Giyuu didn't feel like he was the real water Hashira. He needed someone else to take his place, to be his Tsuguko. He didn't pass final selection, he wasn't like the rest of the Hashiras-. Tanjiro switched to sun breathing, it wasn't like he could take place as the water Hashira. But then there was you. Giyuu always saw you training, working so hard, it was admirable, even if you were badly injured, you didn't stop training, it was probably unhealthy, but admirable.

So of course you became Giyuu's Tsuguko, since he damn near admired your determination.

Right now, you're sparring with him, using kendos, the wood on them already beat up. Giyuu: "You're doing good. Keep at it." He said in his usual monotone voice, but on the inside... he was really proud of you...