While loyal to the Empire at first, after being nearly executed by Fonse Kagatie, Tassilo begins seeking to usurp him as ruler of the Empire.
Tassilo Vago was placed in charge of overseeing the construction and defense of the Zanscare superweapon, the attack satellite Keilas Guilie. Once the satellite was completed, Tassilo intended to use it to bombard the Earth in order to force the Earth Federation to submission.
However, before the satellite could be used against its intended target, it was hijacked by the League Militaire. His fleet devastated by the League Militaire forces, Tassilo was rescued by Zanscare's ace pilot Cronicle Asher, though after being brought back to the Zanscare capital of Amelia, Tassilo was sentenced to be executed by Kagatie for his failure to defend the Keilas Guilie.
As Tassilo was prepared to be executed alongside League Militaire pilots Uso Ewin and Odelo Henrik, he received an opportunity to escape when the League Militaire launched an operation to rescue their two captured pilots.
Tassilo later reemerged as the commander of the fleet in defense of Zanscare's newest superweapon, the Angel Halo. Having lost his respect for the Zanscare leadership after they tried to have him executed, Tassilo began seeking to usurp control of the Zanscare Empire.
Boarding the Angel Halo alongside several forces loyal to him, Tassilo took the Halo's power source, the figurehead of Zanscare, Queen Maria Pia Armonia herself, hostage. Bringing the Queen back to his flagship, the Shubaten, Tassilo attempted to escape with his forces, planning to either seize control of the Zanscare Empire or create an entirely new empire with Maria as his figurehead.
Eventually, the Shubaten was confronted by Uso, piloting his V2 Gundam. When Queen Maria pleaded with Uso to destroy the ship, Tassilo killed her. Mocking Uso as being too soft, Tassilo was killed when Uso destroyed the Shubaten's bridge with his Gundam's beam saber, being vaporized in the explosion.