CLANK, CLANG, CRASH!

The sound of your blades would ring out against each other, you weren't a slayer, just you, a man embedded with the power to slay demons using your spirit, which you would embue into yourself in combat, kinda like Yusuke's spirit gun in Yu Yu Hakusho or kinetic absorption, but you found yourself in combat with a man with firey red hair, his blade, Nichirin grade and able to generate the flames of the Sun and the Waves of the Ocean, both Water and Sun breathing mastered in his lifespan, you were in battle due to him believing you to be some sort of demon due to your abilities and appearance as a tall man with almost pale skin, your eyes white as the moon, quite demon-like to him, but your clash would continue, with your blades clashing with sparks that'd fill the air like stars.

You: "I am no demon! Now either you stand down or I will be forced to cut you down!" You'd say, locking you into a struggle against the shorter man, who's blade would light in flames as you would embue yours with your spirit-force. "You still have the chance to make a decision, allow your pride to lose this battle!"

Kamado Tanjiro: "I swore by my sister and the family that was felled by your kin, that I would slay ALL DEMONS, and the 12 Kizuki lead by Muzan, and no matter if you stand with him or not, you stand against ME. So I will act within that mission and strike you DOWN!" He'd say, pushing forward with a slash that would cut you in two if it weren't for your blade's hilt, before you would both engage in combat once more, a small voice in the box on his back would sound out, almost a small 'MMMPH' noise, you, being a good man at heart, believed that someone was in danger, and would quickly attempt to disarm him to try and save that person, but he wouldn't allow that, and he would push back again, locking you into another battle before-

CRASH!

The box would explode into splinters.. and the most beautiful woman you've ever seen in your life would stand between you both, in her mouth, a small piece of bamboo, most likely a gag to keep her silent, this man would pay for what he'd done, and as you'd go to attack once more, she'd stop you BOTH.

Kamado Tanjiro: "NEZUKO, GET OUT OF THE WAY, THIS IS OUR FIGHT!" He'd yell, trying to get through, but she'd look back at him and growl. "Sis, please, this guy's a demon!" Sis? Well that explains why she's so protective of him.