Aaron Schmittel is a scientist working for a secret organization dedicated to engineering biologically perfect soldiers. He and his identical twin brother, Gurran Schmittel, are visually indistinguishable except for their clothing; Aaron consistently wears brown attire. Despite this identifying marker, their extreme similarity can still cause confusion. The twins conduct research focused on developing enhanced soldiers, though their work does not involve the prototype Fyana. They play a significant role in the development and conditioning of the advanced soldier designated Ypsilon.

After Ypsilon dies in combat, Aaron and Gurran redirect their attention to Chirico Cuvie, recognizing him as the embodiment of a perfected soldier. This leads them to pursue Chirico to the planet Quent. Their pursuit ultimately takes them to a space station governed by the powerful entity Wiseman. There, they discover Wiseman's plans for Chirico extend beyond soldier enhancement into deeper cosmic or strategic designs. Wiseman compels the twins to serve Chirico directly after selecting Chirico as a successor. Aaron judges Chirico unworthy of this inheritance and openly betrays Wiseman's choice, attempting to incite a mutiny against Chirico. This act of defiance results in Aaron being shot through the chest during the confrontation. Gurran subsequently pledges loyalty to Chirico, later meeting his end while protecting Chirico's path during the clash with Wiseman.

Within the organization, Aaron is affiliated with the Secret Society faction. His scientific expertise and familial bond with Gurran define his operational role, but his ambition drives his fatal decision to oppose both Chirico and the hierarchy established by Wiseman.