Sion, a strategic leader within a rebel faction challenging the E=X Bureau and its commander Bishop Won Dai, operates in a futuristic city dominated by the System. Embedded within Orange Amusements—a rival organization dedicated to dismantling the authoritarian regime—he enlists skilled hacker Eiji Takanaka, testing his capabilities through simulated spacecraft trials to evaluate his potential to awaken Eve, an artificial intelligence tied to humanity’s survival.

Severely wounded during a clash with E=X forces, Sion discloses his true mission: thwarting Project Heaven, Won Dai’s scheme to launch the city into space while sacrificing its inhabitants to preserve Earth. He directs Eiji to uncover Eve’s hidden stasis capsule beneath the city, a key to accessing the Bahamut supercomputer and exposing historical secrets of the Megazone colony ships.

Assuming command of Orange, Sion redirects its resources to publicly expose Project Heaven’s grim purpose. In the final uprising, he orchestrates assaults on E=X’s infrastructure, crippling their network and sabotaging the city’s core systems. These efforts enable rebels to fracture the System’s control, though Sion succumbs to fatal injuries inflicted by E=X operatives during the conflict.

Recovered historical records and data disks hint at unresolved ties between Sion’s mission and Shogo Yahagi, a pivotal figure in prior Megazone conflicts. While Sion’s origins before the rebellion remain undocumented, his role centers on strategic defiance, leveraging Eiji’s expertise and Eve’s guidance to dismantle the System’s oppressive framework.