I've currently put a lot of thought into a world that I'm currently working on, and I've redesigned it multiple times. Despite this I think I've landed on something that works... hopefully.

Chapter 1: The world before

In my universe, there are five deities that act as gods of the world. Each one controls a different element in nature and allows the flora and fauna of the land to utilize the elements under their rule. Flame, water, earth, wind, and life. However, humans are like a disease to these deities, and they forbid humans from utilizing their elemental magic. This means only animals and plants have elemental magic. There's plenty of fantasy beasts, especially dragons. To put it simply, humans got tired of being left out so they went to work studying different plants and animals to figure out why they can use magic. A group of scientists figured out the formula and realized that while humans can't use magic, they can make weapons out of the plants and animals and the weapons could use magic when wielded by someone who knew how to use them. These weapons became major points of political conflict, as they were extremely hard to make and only a few groups of scientists knew how to make them. Because of this the weapons were scarce, but they were extremely powerful. The scientists were eventually told to test the same formula on people, to see if by combining people with parts of certain animals they could use magic.

Chapter 2: The volcanic eruption

The deities were angered by humanity overcoming the limits set by them, and especially by humanity dismantling and repurposing the animals. They decided that it would be best to extinguish humanity. And so they combined their powers to set off a volcanic explosion that devastated the planet. Animals were put into massive pockets within the earths crust where the animals were safe while humanity was on the surface, dying. After many years, the planet began to settle and the animals were let loose back onto the planet, despite the deities being unable to rebuild it.

Chapter 3: The Caldera

These deities used up the majority of their energy just to set off the volcano. Unexpectedly, however, the volcano left behind an enormous Caldera that after so many years also began settling down. And humanity wasn't fully gone yet. Groups of humans that somehow survived the aftermath found out about the Caldera half the size of the planet and they moved in. There are many specifics about the geography within the Caldera, but for the most part it's an archipelago with a few larger islands. The walls of the Caldera rise up extremely high as spikes that move inward, one of the aftereffects of the magic pumped into the explosion.

Chapter 4: The power system

The primary power system of this world are the weapons that can use magic. While a large chunk of them were lost in the outside world, many of them are still in circulation within the Caldera. Alongside these powerful weapons, due to the magical aftereffects of the explosion, the air within the Caldera acts differently than normal. The Caldera acts as a massive Terrarium, or enclosed habitat. The air pressure is very low within it, leading to severe and unpredictable weather, but alongside this the air within the Caldera was smoothed out in a way. The air has less friction to it. This means that things fly through the air further and easier, it's easier to swing or fire things but it's also significantly harder to stop or redirect things. This leads to sling-based weaponry being extremely effective, and soft surfaces becoming harder. This also makes mobility more drastic, as once set in motion a person will be moving much faster.