Sayuri Michinaga was Sara Yuki's former classmate at the Space Officer Academy, initially known for her timid and reserved nature. After the war began, she pursued advanced studies, earned a doctorate in computer engineering, and developed a markedly confident demeanor. This transformation was so significant Sara barely recognized her upon their reunion. Sayuri reconnected with Sara just before a major incident involving a destructive entity suspected to be a remnant of the defeated alien empire. During the ensuing battle, she proactively supplied Sara and the Cyber Beast Force with critical technical data and tactical analysis on the creature. However, the conflict caused catastrophic collateral damage, destroying Masato Shikibu's family villa and killing his father.

Investigations later exposed Sayuri's deeper role in destabilizing events. She had created an advanced, sentient supercomputer designed to consume and process vast data. Her stated goal was to use this technology to seize global control, citing the perceived tyranny and corruption of existing governments as her justification. Unknown to the protagonists, Emperor Muge Zorbados, believed destroyed, orchestrated her actions. Muge exploited her technological ambitions, ultimately possessing her mind and body to advance his plan to collapse reality into dimensional space. As part of this scheme, Sayuri captured Sara Yuki.

Her role culminated as an antagonist directly opposing the Cyber Beast Force when they mobilized to stop her plan and rescue Sara. Her actions and technological constructs ignited the central conflict, positioning her as a key figure whose personal history and expertise became instrumental to the resurgence of Emperor Muge Zorbados's greater threat.