Yuu Kajima, an Earth Federation pilot from the start, took part in the Battle of Loum. In late U.C. 0078, he discovered a mostly intact Zaku inside a colony, which significantly benefited the Federation's V Project. Yuu leads the Marmot Team, an experimental corps testing new technologies before they are mass-produced for the Federation Forces. During one sortie, his team encounters the RX-79BD-1 GM Blue Destiny Unit 1, attacking both enemies and allies. When it targets them, Philip and Samana are quickly defeated, and Yuu barely manages to drive it off. Later, the team faces a Zeon mobile suit with similar combat tactics, but the blue GM appears and drives the enemy away just in time.
Back at the base, Yuu is assigned to pilot the GM Blue Destiny. Despite the severe mental strain caused by its EXAM System, he becomes highly proficient with it. Yuu and his team later participate in the Federation's effort to recapture California Base, where Yuu uses the GM Blue Destiny to prevent the Zeons from launching a nuclear missile. However, he is soon attacked by Nimbus Schterzen in the MS-08TX(EXAM) Efreet Custom. During the fight, the EXAM System's voice reveals itself as Marion Welch, a young Newtype girl who assisted in creating EXAM. An experiment gone wrong put her in a coma, imprinting her soul on the machine. The EXAM System grants surrogate Newtype powers to any pilot, but most have been driven insane by Marion's attempts to communicate. She begs Yuu to destroy EXAM and free her spirit. In their duel, Yuu and Nimbus cut each other down simultaneously, destroying their EXAM Systems.
However, Yuu's mission isn't over yet. He meets Professor Chlust Morses, who turns out to be an insane xenophobe paranoid about Newtypes taking over. Morses justifies EXAM as necessary to keep non-Newtypes dominant. As they inspect the newly completed RX-79BD-2 Blue Destiny Unit 2 and RX-79BD-3 Blue Destiny Unit 3, Zeon special forces attack, allowing Nimbus to hijack Blue Destiny Unit 2 and kill Morses. Nimbus escapes to space, with Yuu and his friends pursuing him using Blue Destiny 3. The chase leads to Side 5, where EXAM was first developed, culminating in a final showdown. Nimbus declares himself the only worthy user of EXAM and tries to kill Yuu. Once again, they strike each other down simultaneously, but this time Nimbus is killed, while Yuu drifts in space until his team rescues him.
After these events, Yuu continues serving as a Federation soldier throughout the One Year War. He remains with the Federation during the Gryps Conflict and the first Neo Zeon movement, eventually joining Londo Bell during the second Neo Zeon movement. His actions piloting Blue Destiny 1 earn him the nickname "Blue Death." It is revealed that Yuu was among the RGM-89 Jegan pilots who helped push Axis back at the end of Mobile Suit Gundam: Char's Counterattack.
