Melchisidec, commonly called Melchi, serves as a mechanic aboard the *Libertad*, combining technical expertise with an eccentric personality. They frequently collaborate with their colleague Carmichael, focusing on maintaining and repairing military technology, particularly the specialized mecha units known as Strains.

Melchi discovers an abandoned Mimic unit—a biomechanical device essential for piloting Strains—and integrates it into a porcelain doll later named Emily by Sara. This doll becomes crucial when Sara's original Mimic is destroyed, enabling her to pilot the Ram-Dass Strain. Subsequently, Melchi and Carmichael rebuild the damaged Ram-Dass in a storage area, preparing it for deployment. During testing, they utilize the Emily doll as the Mimic unit, allowing Sara to interface with the Strain despite its lack of biological keying to her. This success permits Sara's return to combat, though command initially resists reinstating her.

Melchi exhibits a distinct, often egotistical or eccentric personality that sometimes causes friction. They habitually rebuke Carmichael with the phrase "Shut up, Carmichael" during disagreements or teasing. Despite these quirks, their superiors tolerate Melchi's behavior due to their indispensable technical skills, proven by the vital restoration of the Ram-Dass for battles against Deague forces.