Muzan Kibutsuji

                                    

                                          
Edited: May 27, 2021
                          
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With a powerful swing of Nezuko's leg, she targets one of the demons. Instead of hitting it, her leg hits the ground causing pieces of dirt to scatter everywhere and dust to block everyone's view of the demon. When dust disappeared, no demons were seen.
                          
The other demon only laughed at the scene before sinking into the ground. Nezuko chased after it but was stopped by Tanjiro.
                          
"Nezuko! Don't chase after him and get back here! Come to us." Tanjiro softly commands her. Being the obedient girl she is, hops in your direction but the demon suddenly appeared.
                          
"Ne-chan! Watch out!" You warned her. She successfully dodged it by doing a flip, landing gracefully on the ground, and finally made it to you.
                          
Getting distracted by the scene you didn't notice the black water underneath you. Before you even had the time to react you were suddenly pulled from down below.
                          
"Ack!"
                          
"(Y/N)!" Tanjiro called for you, but the black water reappeared below him, trying to capture him as well luckily he was able to jump away from it. Tanjiro was now separated from Nezuko and the black water keeps getting bigger and bigger, trying to pull Tanjiro in.
                          
"Nezuko! I'm going underground to save (Y/n) and slay the demon! I want you to protect those two." He told her looking directly into her eyes with his hard gaze before softening, "You can do that, right?" He softly asked her. Nezuko nods. Tanjiro took a step forward into the black water, his foot sinking before his whole body.
                          
'This is a swamp..it's so dark in here.'
                          
You thought before a bunch of yukata and kimono came into your view, floating in the water. 'And these are... Are these girl's clothes?'
                          
All of a sudden, you heard another sound coming from above, you gripped your sword and prepared to attack but the mysterious figure turns out to be Tanjiro. You were relieved and immediately swims next to him, and focused on your surrounding.
                          
The water was rather murky and heavy but this was nothing compared to how you were trained by Urokodaki. Maintaining your breath was an easy task for you.
                          
You slightly smile, 'I can try out some of the breathing techniques here!' You closed your eyes and focused on the noise that was approaching you. Opening your eyes you got ready to attack but just as you were about to slice the demon, it expertly changes direction at a high speed.
                          
'So they can move like that inside this swamp? But it doesn't matter! I kinda know how to attack them like that...' You turned your head to look at Tanjiro. He saw your gaze and nodded his head, knowing what you were trying to say. 
                          
Twisting your upper and lower body, you raised your sword and waited for the demon to come near, enough for you to slash. Closing your eyes you waited for the opening thread to appear. 'Here it comes! Total Concentration! Water Breathing...'
                          
Both of you slash your swords into the water creating a powerful and violent whirlpool. 'Sixth Form! Whirlpool!' The two demons couldn't escape because of the force and got their bodies dismembered.
                          
Tanjiro saw the demon's collection of hairpins and immediately grabbed it. By now both of you were lacking air and needed to breathe. Swimming into the surface, the first scene that you saw is when the demon's about to jab its hand into Nezuko's face.
                          
With your light body, you were faster than the demon and smoothly sliced off its right arm before it even made it to Nezuko. "How dare you hurt Ne-chan!" You angrily said. Tanjiro appeared from behind and cleanly sliced off the demon's left arm.