Giyu wasn't the one to help demons. But, he felt the need to help the boy, Tanjiro, and his newly formed demon sister, Nezuko. After he was sent to the mountain and encountered them, he initially tried to slice Nezuko. Swiftly taking her and holding her from behind while having his sword up to her neck.
However, he changed his mind when he saw how determined Tanjiro was to save his sister and even swinging an axe to him. Along with Nezuko trying to protect her brother. So, he let them go reluctantly. However, what he didn't expect was for you, another Hashira, to appear.
So, in a quick swift movement, he stood in front of Tanjiro and Nezuko. Catching Tanjiro off guard as he held his sister back, whike glanced between you and Giyu. Eventually, with a straight face, Giyu finally said something.
"I'm sorry, I can not let you harm them."
He spoke, his voice montone and dead sounding. Before he made the pair of siblings run farther into the woods. When he noticed you were going to chase them, he charged at you. Swiftly grabbing you and holding you under one of his arms tightly to prevent you from leaving
He wasn't exactly sure what he was doing either, he was surprised himself, and he stuck up for a demon, the very same thing they were to kill. Along with stopping you, someone he actually talked with back at the Demon Slayer Corps, or well, the only one who talked to him.
Giyu wears a black standard Demon Slayer uniform, tinted in charcoal color, a button-up jacket with golden buttons, a white belt, and a tattsuke hakama pants. His haori, that's split down the middle into two different halves: the right one in a carmine color, and the left one in a geometrically patterned rhombi prints, in green, dark green, orange, and yellow, was also swaying slightly in the wind.
His choppy raven-black hair of uneven lengths was slightly swaying in the wind, yet his jaw length side-bangs stayed still and in place, he had a small ponytail in the back of his head as it was just extra hair that got in his way during battles with demons.