A galactic beast that suddenly appears from an ominous light in the skies of Hoshimoto City. Its appearance is similar to that of Digelos, so it is first mistaken for it at first. However, as the three horns come into sight, it becomes clear this is Trigelos, the galactic beast.

At first it does not move, simply floating in place. However, as if reacting to Yuma, it descends to the ground. Its horns start to reverb, releasing sound waves. In response, Yuma’s chest starts to shine and Trigelos is drawn to it.

It’s almost as if Trigelos exists solely to defeat Ultraman Arc, countering every attack with precision. Arc’s unarmed attacks are completely blocked, and even solid hits are useless against Trigelos’ hard exterior. When Arc uses the Arc Eye Sword, Trigelos overwhelms him by transforming both arms into twin blades of light. Even the Arc Finalize is deemed useless, as Trigelos releases a beam from its own head that neutralizes it. Not only that, but it is so familiar with Arc's armors, that when Arc challenges it for a mid-air fight using the high speed of the Luna Armor, it brings out a half-moon shaped object (the Trigelos Hoop) from the shimmering air. With it, Trigelos is able to increase his speed and counterattack.