While his physical strength is lacking even in comparison to many standard Zoanoid models, Gaster earns his Hyper-Zoanoid status based on his armaments. Like Panadyne, he can produce chemical fluids within his body that react violently when combined, producing powerful explosions. These liquids can be discharged from nozzles on his forearms, but not only that, they can be contained within the organic darts mounted on his massive shoulders. Gaster's shoulders are turrets that can launch these darts like missiles and he is capable of guiding these projectiles telepathically.
In human form, Gaster has long, pinkish hair and has pointed ears.
Gaster and the Hyper-Zoanoid Team Five first appear when the Guyvers set out to save the Segawas and Fumio Fukamachi from Relic's Point. During this first engagement, Gaster prevents Guyver-III from using his Mega-Smasher by firing a missile straight into the beam emitter and detonating it. Not long after this first conflict, he and Derzerb are dispatched by Dr. Barcas to attack the Guyvers' hideout. Thanks to Murakami, however, the Guyvers' companions manage to get away since Murakami's telepathy almost coerces Gaster and Derzerb into killing each other.
Much later, when the renegade Aptom invades Relic's Point, Gaster supervises an observation post while Derzerb and ZX-Tole hunt for Aptom. Much to his horror, Aptom has duplicated himself and one of his clones, disguised as a Cronos soldier, attacks Gaster and absorbs him.
In the OVA, Team Five accompany Commander Guyot when he assumes control of Cronos Japan. When the group attack Narisawa High School, Gaster is killed by Guyver-I, who uses his sonic blade to cut into Gaster's fluid sacs that produce his liquid explosives. Gaster is drenched in his own chemicals which react and explode, destroying him.