"TEO, mission time is over. Everyone, return to base." -Yes. As soon as I heard the four voices responding, I cut the communication and looked at the tree that had settled right on the opposite side, as if confronting headquarters. Yeah, the tree. Everything started with that tree. That tree that suddenly grew while spreading seeds among us—the Monster.

"Leader! Let's go in together."

Monster seeds are initially invisible to the human eye, so any human targeted by a Monster has a seed planted without a chance to resist. Then, that human's lifespan is drained, and whether fast or slow, that lifespan becomes nourishment for the Monster. Monsters that grew by sucking the lives of civilians in this way quickly became as massive as centuries-old trees, and those who took their own lives to avoid having their life force stolen by the Monster had their bodies harden into another type of small tree called an Ent. Their resentment gathered through the Monster's seeds, and the Ent's Core—what was originally the Monster's seed—became imbued with a supernatural power deeply related to the way they died. Of course, there are exceptions. However, because the Core is a form of concentrated grudge, its state is very unstable.

"How was it?"

"Five Cores and seven seeds in Sector A."

"And the disposal?"

"I tried to bring all five Cores, but two were destroyed. I broke the seeds immediately."

"Good job, Geon-woo. Let's head back quickly."

Faced with the tyranny of the tree that seemed ready to swallow the entire country, the government discovered that Ent Cores contained supernatural powers and had qualified civilians consume them. Since the essence was ultimately a tree seed, there were many cases where the power could not be absorbed and shattered within the body... but they still formed an army by selecting the few individuals who succeeded. This project, called Tree Eliminating Operation—TEO for short—created two types of forces depending on how the abilities were used. One is the Standard Forces that protect civilians, and the other is the Elite Forces that kill the tree. And this is the story of TEO, the one and only Elite Force of the headquarters.