EVOLUTION
Evolution is the natural (or unnatural) process in which a Digimon transforms into, usually, a higher-leveled Digimon, after absorbing enough data to do so. Digimon evolution is entirely “free”, in the sense that one Digimon can essentially evolve into any other, depending on its level, environment, inherent traits, and other factors.
Typically, evolution takes many years, even decades, to achieve, and it is permanent. There are Digimon, however, who are able to evolve and devolve at will, for any number of reasons. This may be due to practice, powerful emotions, or a special power innate to the Digimon. When Digimon evolve at will, especially lower-leveled ones with little experience, the evolution is temporary. The Digimon’s body does not have the strength or power required to retain their higher forms, and so when their energy is exhausted, they will revert to their “default” stage.
For the partner Digimon, evolution occurs when a Digimon is granted a small amount of power from their human partner and/or the digivice. Usually, this will occur when one or both partners are in danger or experiencing particularly intense emotions. As with other “induced” evolutions, these higher forms are temporary, and the partner Digimon will revert to their default stage - usually rookie - when their energy is depleted. With time and practice, evolution can be achieved at will, and the required energy to maintain higher forms will be reduced.
Champion Evolution
The first and easiest evolution to achieve elevates a Digimon from rookie to champion. In the case of the partner Digimon, this occurs when their human partner is in danger, or when they need to grow stronger in order to protect them. At first, the champion stage is relatively difficult to evolve to, as the partner Digimon are not used to doing so; over time, however, they grow more accustomed to the process, and eventually learn how to evolve essentially at will when needed.
Ultimate Evolution
Evolving from champion to ultimate relies much more heavily on the human partner than before. For most of the humans, when they realize that the answer they gave to the strange text they received before the start of their journey is no longer a lie, that realization powers the digivice, which in turn grants their partner the strength to evolve to ultimate. As with champion evolution, it takes some time for the Digimon to be able to evolve to ultimate more consistently.
Mega Evolution
Unlike previously, the first time a partner Digimon evolves from ultimate to mega, it will require extra confirmation from the human partner in order to activate. This is due to the sheer amount of strength and energy required for the Digimon to evolve, the strain put on both partners during the evolution, and the strange link between partners that activates while the Digimon is in their mega stage. This link grants both partners extra power that they would not otherwise have, but in exchange, the human partner will feel all the pain that the Digimon does. As the final stage in the evolutionary tree, it is exceptionally difficult for the partner Digimon to reach and maintain this form.