The fifth unit of the Earth Federation's Tsentr Project, the Medius Locus is a real robot that serves as the testbed for armor made from Lasmunanium alloy, which has the ability to self repair and evolve. It isn't equipped with a Terminus energy engine for fear of its effect on the Lasmunanium. The Medius Locus is also loaded with the advanced artificial intelligence AI1 All-In-1. It's designed to be a well-rounded machine and is equipped with a coating sword and a divided rifle.
The Medius Locus is stolen by Eldy Middi and Albero Est. Albero serves as the main pilot while Eldy supervises AI1. Albero's former subordinate Hugo Medio and Eldy's former student Aqua Centolm give chase in the Terminus energy-powered Tsentr unit. Albero and Eldy align themselves with several factions seeking to conquer Earth in order to let AI1 gain experience. After many encounters with Hugo and Aqua, the Medius Locus eventually acquires the TE engine of the other unit.
The TE Engine greatly powers up the Medius Locus, causing the Lasmunanium to evolve and change the mech's shape. The Medius' second form is that of a super robot. Its armaments are eight riot boomerangs, two spiral fangs, and the Terminus blazer. It is able to create a TE Sphere barrier thanks to the TE engine. It also has the ability to create Y??-01 Telgum and Y??-02 Flonnes from Lasmunanium. AI1 continues to gather combat data by fighting many enemies. As the apocalyptic events of the Tuning and the Human Instrumentality Project get underway, the source of Mutron energy, the Star of La Mu, appears. Eldy has AI1 absorb the star, which causes the Medius Locus to evolve further.
The third form of the Medius is far different from the previous two. The machine now resembles a giant monster and attacks with brute force. Eldy and Albero have no control over this form; only the berserk AI1 does. AI1's core unit continues to expand and eventually absorbs the machine.