The story unfolds on Endra, a hidden realm situated beneath the Earth's surface. In this other world, a colossal gem called Adamas illuminates the sky while seven-hued ribbons drift through the air.
One day, Shun Asanaga—a cheerful and optimistic 15-year-old middle school boy from the "Land Above"—finds himself in this mysterious place. He came across a peculiar crystal at his father's scientific business firm, and the instant he touched it, he was transported to Endra.
There he encounters Prince Emirio, who harbors a deep hatred for the reigning King Deruzain and has just turned 16 within Endra's castle. Having reached the age eligible to claim the throne, Emirio finally takes up arms to pursue vengeance, yet the gap in their power proves too great. Captured and thrown into a dungeon by Deruzain, Emirio feels utterly crushed. But suddenly, the prison walls warp and twist, and Shun materializes before him.
Two youths now inhabit Endra—one yearning to return to his original world, the other seeking retribution. The future that lies within the grasp of these two boys raised in separate realms…
