I'm making a D&D 5e module from scratch (essentially homebrew) because I had an idea in which magic doesn't exist, so here we are.

Whatever genre D&D is considered

Pretty normal, though there are some exceptions due to Soul abilities and the occasional "What The Fuck" factor.

There isn't a magic system. Instead, there is a Soul system. Depending on what Soul a being possesses, it is capable of doing certain things. Of course, this system can still lead to many shenanigans without the excuses of weird "it's just magic" flaws.

The level of technology depends on the region, though all of the existing technology is up to the 16th century (worldwide, not just capitalist colonial bullshit).

A very intense dream and peer pressure.

The general dream:

There were normal people, those who have souls and still have bodies. I was one of those people, until a Soul Eater pack showed up in my neighborhood. They looked like normal people, they even had souls of their own, but their job was to consume the souls of others. To do so, they were grabted the ability to shapeshift. They were originally created for the purpose of hunting and consuming bad souls, those who have become corrupt and lost their humanity. However, most souls are in a greyscale of morality, and eventually the Soul Eaters gave up trying to eat only bad souls and upgraded to eating any soul they could get their hands on. So I had a pack of that shit in my neighborhood. They break into my house and decide to take everyone hostage, as snacks for later.

In captivity, I'm trying to figure a way out, and I get caught. I'm cornered with no help in sight. There's only one thing left to do--pray. I sent out a plea to any higher power willing to listen. ... And I got a damn response.

I ended up giving the being my soul in exchange for being able to fight the Soul Eaters on an even playing field. I became a Soulless. Rare and often outcasted from society, Soulless are people who still live on even though their essence is gone. This is for one of two reasons, either they entered a bargain or they possessed a spirit stronger than their soul, allowing them to live on. Well, because I sold my soul in a bargain, I gained some things from it, such as literally not being able to die until my mission (killing all Soul Eaters) was completed.

Back to the story, I sold my soul to something, allowing me to not be completely useless against the Soul Eaters. It also surprised them when they started to transform to do the consuming, and realized there wasn't anything there to consume.

Not one of them was left standing. But instead of a hero's welcome as I released my neighbors from captivity, I was treated like a monster. I took their words and left.
I ended up in a fantastical world that looked nothing like the one I had been ostracized for protecting. It was beautiful and full of color and life. I had tracked a Soul Eater into a place most video games would call the Deep Woods. I found it--it was alone in the middle of a sun-dappled clearing, napping in the soft grass as a bubbling spring provided decent enough noise cover for me to approach undetected (or at least I thought). It was awake, and turned over to greet me as I got close. His true for resembled that of a bipefal red panda, but less cute and more teeth. Perfect to eat someone's soul. But instead of pouncing on me, he waved over to the spring and implore I quench my thirst from its pure water.

After he explained he had no interest in doing his job and eating souls, I explained that I was there to kill him for doing just that. It was a tense talk, ending with me dragging him along. I get to keep my eye on him and he gets to live (for now).
Next up we visit a water temple ruin. It seems as though it's been completely abandoned for a while now. Keep in mind, seems. While exploring the left wing, I run into a bed chamber that isn't so empty. What I thought was a pile of clothes soon animates into a being. Another Soulless, like me, but this one didn't sell his soul. His spirit and determination to keep living outweighed losing his own soul, so now he continues to shamble on. He doesn't have a purpose like I do, he's just running on borrowed time. Not bearing to leave him alone in his decrepit temple, I decide to take him with me.

Eventually in my hunt for more Soul Eaters, I come across a small village, from which I am "gifted" a regular girl. In reality, the townspeople think we're all monsters and throws her out as a sacrifice to keep us at bay. I instead ask her to join us. It doesn't take much convincing for her to say yes.
After what seemed like days, I received news of a swarm of Soul Eaters gathering in a popular vacation spot, where the water flows lazily and shade is abundant.

This is it.

However, when I arrive I am not greeted by Soul Eaters, but instead welcomed by employees. I get the others a room, tell them to enjoy their stay, then drag the toothy Red Panda Soul Eater with me to investigate what the hell is going on. I was right to be suspicious.

The swarm of Soul Eates was acting like an underground trafficking ring, even having a few staff on the inside to help maintain secrecy. On the way back to the room, my Soul Eater friend and I get into a fight, and he dramatically runs off. I leave him be and return to the room where I discover several Soul Eaters lying in wait for me. I interrogate them before killing them, learning that they kidnapped the girl for her soul and turned the other Soulless into their work slave.

I charge in alone, pissed off and murder on my mind.

I wake up in the middle of the fight.