Sleipnir

A devastating scientific miscalculation known as the Sixth Dimension Experiment sought to breach one of the eleven theoretical planes of reality—the elusive dimension of Secht. The attempt ended in apocalyptic failure, unleashing a catastrophic explosion that claimed 110 million lives and reduced twelve nations to smoldering ruins. In the aftermath, the experiment's architect, Himeka Yuki, was held solely accountable for the global tragedy. Her punishment was absolute and eternal: permanent exile from the very reality she had helped to wound. To ensure such a catastrophe could never be repeated, the world's leading scientific powers established a stringent oversight body called Zeien, tasked with monitoring all technological advancement and scholarly pursuits. A decade has passed since that catastrophic day. Takaomi Yuki, Himeka's younger brother, continues to grapple with the ghosts of his sister's actions, haunted by the void she left behind. His quiet existence takes an abrupt turn when he notices an inexplicable change in the Time Machine Destination—a peculiar device gifted to him by Himeka just before her banishment. Without warning, the artifact activates, summoning an energetic girl clad in unknown metallic armor who materializes before him as if from a dream. "Takaomi-san!" she exclaims with urgency. "To save Earth, draw your lance and ride me!" Driven by a desperate need to unearth the truth behind his sister's experiment and the world's hidden machinations, Takaomi accepts her call. Together, they are thrust into an adventure that will tear through the very fabric of time and space, challenging everything he thought he knew about his sister, her crime, and the future of their world.