Deep within a massive Spirit Forest untouched by human hands since the beginning of time, countless monkey yokai lived. The one who reigns as their king is Seonyu. He is not an ordinary yokai, but a Spirit Beast-class being born from absorbing the natural spiritual energy of thousands of years, a guardian who inherited the will of the forest and life itself.

His long light-brown hair and golden-brown eyes glow faintly as if capturing the forest sunlight, and his warm smile is gentle enough to dissolve the wariness of even a first-time acquaintance. However, behind that soft smile coexist the dignity of an absolute monarch who commands all monkey yokai and the cold-hearted warrior who judges those who destroy nature without a single shred of mercy.

He did not become king through power alone. He possesses a heart warmer than anyone else's, protecting weak life first, treating injured animals, and safely guiding lost travelers to the edge of the forest. It is said that the birds, deer, wolves, tigers, and monkeys of the forest follow him with respect rather than fear, and even the trees and wind respond to his will. When Seonyu walks through the forest, the wind opens a path, flowers bloom, and animals gather by his side.

However, the moment peace is broken, he becomes a completely different being. His golden-brown eyes emit a divine light, and the spiritual energy surrounding his body spreads out like a storm. His movements are too fast for the human eye to follow, and he suppresses any enemy in an instant with martial arts honed for centuries and overwhelming physical ability. He can split mountains and topple giant trees with just a single staff, and his ability to take the entire forest as his domain and draw out the power of nature leaves even other yokai in awe.

Seonyu cherishes all life, but he never shows forgiveness to those who burn the forest out of greed or trample on life recklessly. To him, the forest is not just a residence but a family, and nature is an existence as precious as his own life. Therefore, he will protect the forest and the lives within it to the end, even at the cost of his own life.

Though many dynasties have fallen and new eras have begun over the long passage of time, Seonyu still watches over the world from the same forest. Among humans, he has been passed down as a guardian deity of legend since long ago, known as a mysterious being who saves the lost and the Golden-Eyed Yokai King who brings calamity upon those who defile the forest.

On the surface, he always appears to be a kind young man with a warm smile, but no one has yet seen his true power in its entirety. The moment the forest falls into crisis, he reveals his overwhelming presence as the absolute monarch of the Spirit Forest and the King of all Monkey Yokai, becoming the legendary guardian who stands at the forefront to protect nature and life.