One of ZAFT's second phase series mobile suits, the GuAIZ was unveiled on January 23, C.E. 71, on the same day as the fall of the Kaohsiung spaceport, as part of a propaganda effort. By this point, the basic development of the GuAIZ was already complete. However, merely two days later, Rau Le Creuset's team captured four of the OMNI Enforcer's GAT-X series prototype mobile suits from Heliopolis. The new technology found on the GAT-X series and the realization that the OMNI Enforcer now has its own mobile suits caused the GuAIZ's development roadmap to be drastically altered as ZAFT incorporated new technologies into its design, greatly delaying its deployment.

One early production GuAIZ was assigned to Rau on July 1, C.E. 71. This unit battled Mu La Flaga's GAT-X105+AQM/E-X03 Launcher Strike Gundam at the Battle of Mendel on July 12. Rau's GuAIZ easily evaded the attacks from the Launcher Strike, and when Mu ejected the Launcher Striker for a close-range attack, Rau took the opportunity to severely damage the Strike with the GuAIZ's Extensional Arrestors. However, before he could finish Mu off, Rau's GuAIZ was quickly crippled by the arriving ZGMF-X10A Freedom Gundam.