Tale of the Thunder Breather (Demon Slayer x Reader Insert)

An Infinite Fortress

I turned around the second I heard that instruments sound and to my surprise, I was in a whole new place. It looked like each wall and floor repeated itself and went on and on for what seemed like forever. This sudden change in the environment also triggered my senses to go haywire. It felt like there were so many things... no demons were watching me. It didn't help that I was in the open as well, so I quickly turned and made my way into what looked like a very small room.

The sound of the biwa was heard again, and the floor beneath me gave out, and I went with it falling very quickly. I looked around and saw many demons poking their heads out. A lot of them tried going after me, and I simply sliced their heads off until I found a way to land. I noticed a nearby wall, so I used the decomposing body of a demon as leverage to move towards the wall and shoved my Nichirin blade into the material. It slowed my fall but didn't stop some of the pain as soon as I made contact with the floor below. I didn't even have time to recover before another demon knocked me into a wall. I tried to dodge as it came for another attack, but it cut my arm in the process. I cut its head off and continue through this labyrinth.

It felt colder than normal, almost as if I couldn't breathe right. I brought up my body temperature some more as I used Flame Breathing against the onslaught of demons coming at me.

Another strum of the biwa and I was smacked through multiple walls and into a very large area.

Y/N: Yeah, there goes a rib.

I painfully got up to look at my surroundings. It seemed unnatural that there were no demons here. Still surveying the surroundings, I rub my shoulders because at this point, I'm freezing cold. That when I saw them. The six I saw that day standing in a line. Each with their respective numbers in their eyes.

Seeing them sent me back to when I was a kid and had felt fear. My hands immediately drew my weapon and got into a stance watching their every move.

??: Kill him quickly. You will never have another chance. He will be incredibly upset if you all waste this opportunity.

Said the demon with the sword as it walked away from the others.

Almost in the blink of an eye, one of them moves in for the kill using its fists and martial arts. I managed to dodge.

Y/N: Flame Breathing - second form.

I cut its arm off in an upward motion.

Y/N: Rising Scorching Sun.

Afterward, I quickly stepped back and was instantly met with these blood like sickle weapons moving towards me, so I quickly dodged out of the way and was once again thrown into a wall. I struggled to get up again but quickly managed.

Upper Moon 3: My, you are strong. Even stronger than the last time we met. Say, I didn't catch your name after we killed your brother. Can I ask what it is.

I took a deep breath, still feeling incredibly cold. It seemed like one of the other Upper Moons was affecting the air.

Y/N: You don't deserve to know what my name is.

Upper Moon 3: Hmmm. Shame. Looks like I just have to kill you.

Once again, he tried to punch my face and managed to dodge it at the cost of a sharp pain on my head.

Backing up, I put my hand on the wound and saw blood.

Upper Moon 3: See. That's the power of an upper moon. You might as well give up.

I just looked at it as the blood trailed down my face.

Y/N: Heh. It's kind of pathetic.

The demon seemed to be taken aback by my statement. Veins appeared on his forehead, and it seemed like his markings started glowing a little.

Upper Moon 3: What did you say, brat?

I needed to get away from the cold so I could regain my breathing. I was looking for a way out when I found something.

Y/N: I don't think I stuttered. Like, what's so special about you? You just use your hands as an attack. But this has been fun, but I should get going.

Upper Moon 3: Oh no. You're stuck here forever. It is impossible to get out.

I got into a water breathing stance.

Y/N: Seems like it. But what's the harm in trying. Water breathing - Second form. Water Wheel.

Upper Moon 3 charges again.

In a wheel like motion, I cut through the thin floor into another free fall. But this time, I was faced with other problems.

Multiple fabric sashes and blood Sickles were heading in my direction. I knew it wouldn't be easy, but damn. I cut the attacks as much as I could. However, some of them hit me. I could quickly feel a poison in my system from the Sickles. Thankfully, Tengen had poisoned me greatly in the past two years, so I slowly developed a small resistance, but I could still feel it.

Another strum of the biwa and I noticed multiple corridors were opening and closing, and in some of them, I saw demons traveling between this fortress into the real world. That's my way out.

From out of nowhere, a huge gust of wind knocked me out of my free fall into another room. Suddenly, I was faced with four upper Moon 4s? One was yellow, another was red, and then a green and blue one.

Red Upper Moon: You think you can outrun us?

Y/N: Yes?

I quickly turned around and ran. The red Upper Moon tapped its staff on the ground, and the perimeter of the room went up with electricity.

Y/N: Fine. If you want a fight.

I got into a thunder breathing stance.

Y/N: You got one. Thunder breathing - First form.

I went after the one with the staff in one quick motion and cut off its head. The incredibly surprising and small victory was short-lived as the green one blasted me out of the room and onto another level, and I landed in a bad way.

The impact made me cough up some blood. But I had a clear chance to look around. I heard the biwa again, so I looked for any openings, and there it was, a demon started walking to a way out into the town I was in before this. I jumped off the platform I was on and fell on top of the demon and quickly killed it. There were two more Upper Moons behind me, the one that was making me almost freeze to death and the fish like one. I knew because there were vases everywhere and the cold feeling was back, but even more that, I was getting frostbite just being near it. I knew I wasn't clear yet. I decided that now was my only chance as I wouldn't have another before they would kill me, so I ran as fast as I could. This action costed a bunch of needles embedded into my skin and many cuts from a storms of ice, but with one final push I reached the outside just as another strum of the biwa rung out and closed.

I breathed heavily and fast. The poison from both the Sickles and needles were finally taking their toll, and I collapsed right there. And as my vision was almost cut out, I saw a silhouette walking towards me before I blacked out from the pain and poison.