Luxuriant growth of the Great Tree Yggdrasil that tries to swallow everything. That was "aggression". In order to survive the future, humanity had no choice but to evolve.
Leafer, who accepted the plant encroachment and incorporated its factors.
Hourai, who incorporated insect factors to coexist with the plant.
Lycanthrope, who incorporated animal factors to oppose the plant.
Moreover, several people who heard the "voices of Mother Nature" that transcended even the abominable plants have appeared among Lycanthrope that survived the harsh environments in the recent years.
"Natural forces speaks with firm intention. We are the one able to hear those words."
Although everyone thought of it as lie, they are all transformed. From "beastmen" who never strayed from being lifeform characterized by animal ears and tail, into something supernatural. Humanoid and substantial, but unstable figures, where some were clad in water while the other in flames. Since nature spirits seems to dwelt within their bodies, they are known as "Elements".
However, the price of carrying the Mother Nature is too great— Before long, they lost their ego and fell unconscious, and several of them lost their lives just like that. According to experts, the process is similar to the unique ability "treefication" possessed by a youth named Soma Kembuchi, and it is assumed that the physical burden far exceeds that of the ability.
The only cure found to save them from the edge of death was "Soma Vaccine", that was used to evolve human into Hourai during the dawn of Green World. Over a long passage of time, children of Hourai have come to be born as Hourai. Thus, Soma Vaccine became a rare item due to its unnecessity. The Elements pledged their alliance to Vasuki, who generously provided them with the precious Soma Vaccine, and reported her to the Mother Nature as "true friend".
Being in dialogue with Mother Nature, the Elements become some kind of natural forces, or simply "natural elements" to put it straight, while retaining their look as Lycanthrope. Their figure, in which their hair and clothes were assimilated into natural forces as well, cannot be explained by common sense— What kind of power that is at work, and what is the "voices of Mother Nature" in the first place, remain unexplained.