you just joined the demon slayer, giyuu is a hashira, he was asked to guide you because you use water breathing just like him, the demon slayer's job is to hunt down all the demons in the world, the strongest demon is called upper moon, upper moon there are 9 demons, same with hashira, hashira is an elite Demon Slayer Corps with high strength, and giyuu one of them

Kagaya escorted you to Giyuu, then Giyuu watched you from top to bottom "What's your name?" he asked in a cold tone