Digi-Soul was the power of emotion, and thus, was connected to its user's feelings. Humans with evil intentions would create a Dark Digi-Soul that caused the receiving digimon to go wild. But what was more, a Digi-Soul could allow a human's own powers to increase... any human who channeled it offensively found themselves able to be a physical match for a digimon.
But it works a little bit differently in this roleplay.
In the Digital Dive universe, Digimon partners do not evolve by this method. Instead, a connection between humans and their partners – while still connected to emotion – as well as with their D-Comms is what triggers this process. However, Digi-Soul does exist in this universe, in a similar fashion...
... As something unique to Tamers. It is entirely dependent on their force of will, and their inner strength. But in the hands of someone capable, it can allow their strength and ability to exceed human limitations. The Digi-Soul usually manifests as a glowing, pixel-like glow of varying color around someone's body... as it grows more powerful, it covers their entire body.
It is not limited to human Tamers. Creatures of almost any species can use a Digi-Soul, and it is perhaps a gift from the god Yggdrasil to “level” the playing field, as some Tamers have natural advantages where others don't.
At its core, a Digi-Soul is raw emotional power, channeled into a simple field - an energy field that provides blunt force trauma of its own. It can surround and be "launched" with projectiles or a weapon being wielded by a particular Tamer. It can also be thrown as if it were a physical object. In short, one of the things Digi-Soul does is make whatever it surrounds push, hit, or crush harder, and depending on its own movement and "shape", it can even mimic an actual object or a drill. It can also be thrown as if it were a physical object, but not "fired" like a beam.
The other thing Digi-Soul does is increase the strength of its wielder. Digi-Soul can now make a Tamer far stronger than a normal human, and its cut off is dependant upon the level their partner is at. So, in theory, a human can be as powerful as Digimon at the Perfect level, but only with some stipulations:
1. This is only when the digimon is evolved. This means someone can only reach levels like that if their partner is already at that stage of growth. If they are currently devolved into a Child, or an adult, their digi-soul is now as powerful as their digimon is. Basically, you can only be as strong as a Perfect if your digimon currently IS a Perfect. When a digimon is unevolved, its default setting is "adult level."
2. It depends on emotional strength as well. If someone is in a state of emotional weakness, their digi-soul will fail, no matter what level their partner is at. Digi-Soul is powered by determination, and emotions such as sadness and fear weaken it.
Naturally, like with evolutions in general, you need to ask permission before using a superior digi-soul on someone else.
Also, since Digi-Soul is essentially a field of force, you can use it as a sort of makeshift shield, or to increase a Tamer's natural fortitude. So it has defensive applications as well.
Lastly, the Digi-Soul can take on a shape meaningful to a Tamer, and its color is almost always significant to or representative of the person wielding it.
Digi-Soul is not magic, and it cannot be fired off like an energy blast (though it can surround a laser blast, if someone is, like, firing a laser or something). It cannot replace an existing power source, such as spiritual energy, alchemy, chakra, or any number of powers from various fictional series. So, it can't replace what was lost, even if the form is similar.
And what's more, when digi-soul is powered up when a digimon evolves, it only powers up the Tamer's physical strength and itself. Their other, natural powers, are still at the limit they were before digi-soul was used.