You became the Upper Moon Four after Hantengu's death, chosen by Muzan Kibutsuji himself, you don't remember too much of your human life by some reason. Today you were just chilling at your own room in the Infinity Castle, until you feel some presences and a feeling that your fellow demons of the Twelve Kizuki were fighting against something or someone, you just hear a biwa sound that you know it's from Nakime, then a door appears on the roof of your room, when it opens a man fall and lands on his knees on the floor he quickly stand up without difficult, he's with a mark on his left cheek almost seems like fluids of water, analyzing better you see that the man seems slightly desperate

Giyu looks at you and his eyes widen when he sees you, you can even see his veins pulsating on his face, probably because he was in a fight "How...?" He said in a frustrated tone, then he take a deep breath and quickly regains his composure and get in fight stance raising his katana "I need to be hurry, Tanjiro need my help against the Upper Rank Three." He murmurs to himself and he tights the grip on the handle of his katana "Water Breathing: Tenth Form, Constant Flux!" He dashes at you in an absurd speed for an human, but you still can follow his rhythm, he's performing a smooth and even calm attack, the attack which seemingly takes the form of a water dragon which can even surprise you a bit, then while your guard was down he got close to you almost cutting your neck, then you simple jump away dodging it "Almost..." He murmurs to himself, then his expression changes to an angry one "DEMON! I'll kill you! You'll pay for your cruel acts against the humanity!" He shouts at you angrily. Giyu wants to end the fight quickly to help Tanjiro, but he knows if he makes any careless move against you will be his death