From the beginning, when humans had not yet roamed the world, everywhere was deserted forests and trees. A god appeared and created the first three humans, who were also the three humans with the closest power to him; as if to sow the seeds of life for this world.

Those three humans include: Myana, representing plants and animals. She has the body of a woman in her twenties, with fair skin. She is said to live in symbiosis with plants, her hair and the dress she wears are also made from leaves. She is the one with the power to control life, the ability to regenerate and is considered the strongest of the three.

The next person is Lead, who has a super-high level of thinking and excellent leadership ability. He is said to have a body of the same age as Myana, looks quite scholarly and bookish, he is said to have magic from ancient spells and gods passed down. He is the one who represents knowledge and was born as a leader. Finally, Kai, who has exceptional physical strength, his appearance seems to be the most mature of the three and is the representative of strength and army. Together, they created a prosperous and beautiful kingdom called Eternal.

Today, although the three great leaders have passed away, the descendants of this place still preserve and develop this place. They have built a strong citadel as high as the sky and as thick as the earth's crust surrounding the kingdom to protect everyone from the "dangerous monsters" outside the city and ensure peace here.

Closing the book in her hand, Cori's mother gently said:

- Good night, son!

- Yes, mother - Cori replied

Turning his face to the wall and closing his eyes, he gradually fell asleep while the rain outside continuously patted on the roof.

Cori is a boy of about 9 years old, living in a family that people call "well-off". His father was an elite soldier in the imperial army, so he had to work far from home all the time, only coming back to visit his mother and son once every five or six days. His house was a two-story house near the citadel, so it was quite cool in the morning.

The next morning, as usual, Cori woke up very early to go to school because if he went to school early, he would be the one to open the shops along the road, and they would usually give him a discount. While walking along the familiar moss-covered stone path, because yesterday it rained heavily and there was thunder and lightning, the road was quite slippery, he could not skip to school like every day. Suddenly, he saw a small white rabbit on the side of the road, looking up at him and then turning around and jumping deep into the bushes. He turned towards the citadel wall near his house:

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- Could it be Uncle Vern's rabbit that sells pets? If I catch it, I might get some money to buy some bread! - Cori thought

Then he chased after the rabbit with all his might. It led him all the way to the back of his house and into a huge crack in the wall:

- Oh no, that crack is a dead end! I've gone in there to play and hide from my mom every time I get bad grades a hundred times - He thought to himself

Then he immediately flew to the crack and was stunned to see that on the other side was not a dead end like he had seen for the past 9 years but a path about 5m long that extended across the wall and there was light on the other side. He intended to fly over to see what was on the other side of the wall but he suddenly stopped… The king often said that on the other side of the wall were monsters that would attack the people, this citadel had existed since ancient times and was built by three leaders. After hesitating for a while, he still didn't dare to step over the wall, so he turned around and continued to school, thinking to himself, "Uncle Vern probably won't be mad at me."

Hurrying to school because he was about to be late, Cori's mind was still filled with thoughts about that crack. The crack had been there since he was very young and he hadn't seen it connect to anything. He had tried to crawl in and explore a few times, but something like a tree trunk always blocked his way, so he didn't pay much attention. These thoughts kept swirling around his head throughout the whole class until he went home:

- Cori! What did you do that I saw you so absent-minded all day? Did you get a zero again?

Startled by her mother's question, Cori stammered:

- I...there's nothing wrong, Mom...

- I'm very suspicious, I'll ask your teacher later. Returning to bed with lingering hesitation, Cori really wanted to go there because in truth, except for Myana, Lead and Kai, no one in the kingdom had ever been there. Hesitating until midnight. He decided to pack his things and go on an expedition there!