Once, a mysterious enemy known as "Unknown" suddenly appeared. In response, the "Super Evolution Railway Development Organization," also known as "ERDA," developed robots called "Shinkalion," which could transform from bullet trains to defend against this threat. Taisei Taisei, a second-year middle school student, transfers to Shinkai Academy's middle school division in search of clues about his sister, who disappeared two years ago. Just as he settles in, the Unknown reappears for the first time in ten years. By chance, it is discovered that Taisei has an exceptionally high aptitude to pilot a Shinkalion, forcing him to make the decision to fight. What is the true identity of the Unknown, and what is their purpose? The truth gradually comes to light through battle. The story of the boys' resolve and growth begins now.