General Sylvester commands the Earth Federation's orbital defense force, the Secret Force, enforcing anti-pollution policies and protecting Earth from external threats like space rebellions and alien invasions. From Miracle Base, he directs strategic operations coordinating starships, space fortresses, and giant robots such as the G-Types. His oversight extends to personnel including Dr. Blueheim and G1/G2 robot pilots Charles Danner and Sarah.

After a teleportation accident materializes the virtual robot Laserion, Sylvester conscripts its creator Takashi Katori to pilot it against the Rebel Army led by renegade lunar scientist Dr. Godheim—a pragmatic decision to mobilize resources during crisis. When the extraterrestrial Jack Empire emerges as a greater threat, he spearheads Earth's military response, analyzing intelligence from alien defector Erefan to decipher enemy tactics and weaponry. Throughout these conflicts, he coordinates planetary defenses, deploying ground and naval units against Jack Empire incursions into territories like Hawaii and the Sahara Desert.

Though fundamentally a strategist, Sylvester's leadership incorporates concern for subordinates' well-being, visible in high-stakes interactions with Takashi. He collaborates closely with scientific advisors like Dr. Blueheim to integrate technological advances—including Laserion's Battle Gear enhancements—into combat strategies against evolving threats. Sylvester remains a constant in Earth's chain of command through both conflicts, culminating in hostage liberation and restored security.