This is just a brief look at the power system I'm introducing. You can read it here or just read it when it comes up during the story, whichever you prefer. Some things here are subject to change as I am absolute garbage at explaining things so sometimes I might have to rewrite things to get them the way I want them to be.
Within everything that is alive, resides a pool of energy that is related to one's own life force. This energy is called the Vitality of Life.
This energy linked to our life force has two forms. One form of it is created and stored in our bodies, called physical energy. The other form is created and stored in our souls, called spiritual energy. While these two energies may seem to be vastly different since they are used in different ways, they are still, in essence, two forms of the same thing. Similarly to how water can exist in the form of ice or steam, it is still the same thing. These two energies work in harmony with our body and soul and are essential to life. Due to being directly related to your life force, these two energies can be converted into each other. This happens automatically if you run out of one type of energy, but can also be done manually to keep your abilities in better condition and balance the gap between the body and soul, preventing a disconnect from happening. As long as you have a little bit of either energy, you have the potential to survive. Only when someone loses all their energy will they have died.
A person's strength is directly related to their Vitality of Life, which is made up of both these energies. The physical energy that is produced and stored in your body is able to enhance your body's resistance to outside forces and its overall performance doing physical activities. The spiritual energy that is produced and stored in your soul is able to enhance your soul's resistance to outside forces that affect the soul as well as improve its overall mental performance.
In order for someone to increase their strength, there are several things they can do.
One way is to increase the amount of energy your body and soul can hold inside of it. Having more energy allows you to accomplish more, simple as that. The more energy you have to work with, the wider your range of options becomes. To increase your energy, you have to refine the very things that produce and hold it. In other words, you have to refine your body and soul. There are many different techniques people can use that are made for a wide variety of people to be able to use, like techniques and of one kind of race can use, but everyone is unique, and there are no two people that are exactly alike, no matter how similar they may be, so it is always better if one is able to create a way to do it themselves. Doing it themselves however, isn't easy, and many people use common techniques. This process of training your body and soul that tears at your foundations, then building it back up as you naturally recover, is a universally applied truth to all living beings to increase their strength.
Simply having large amounts of energy won't be enough to sufficiently increase your strength, however. One must be skilled in handling the energy that lies inside of themselves if they wish to grow stronger. Some are simply innately talented at handling their energy, and have no such problems, but that isn't the case for everyone, and even then, there may be a better way than simply doing what just feels right. After all, handling your energy incorrectly can massively waste the amount of energy required to do anything. So having good control over your energy will not only let you not waste your energy, but also let you do more things with it.
On top of increasing the amount of energy you have and your control over it, it is possible to further manipulate your energy to accomplish things you could never do otherwise. One can manipulate energy, changing its properties to match the energies of nature and spirits. With the manipulation of energy, you can create all sorts of techniques, typically referred to as [Arts]. These techniques are how most battle each other, protect themselves against the unknown, and simply progress their everyday lives. There are techniques that allow one to control fire and ice, techniques that imbue their weapons and body with their energy, techniques that manipulate the things or people around them, techniques that make use of items in nature to create concoctions with many effects....
No matter who it is, everyone makes use of [Arts] for everything. This is the rule of the world.
There are many types of races and creatures in the world. Of course, there are also the select few who stand at the top in power. Beings so powerful they live on a separate plane. These beings are those who have ascended to a higher tier. These beings are Gods. When a being is born, they may receive a blessing from a God, showing their potential. Very rarely however, a person can perform an incredible feat that earns a God's favor, thus giving them a blessing. These blessings are proof of having the potential to reach the pinnacle of mortality.
The last way of gaining strength is through a technique known as [Contracts]. This allows a being of greater strength to essentially give their own lesser version of a blessing. It gives the weaker being an increase of strength relative to the gap of strength in between the head of the contract and the recipient. This process requires the consent of both parties.