Director of Kiriyama Heavy Industries and responsible of the creation of the Thunderclap Armas, he was childhood friend of Reiji Moritsugu, of whom greatly respected his ideals of justice. Apparently however, over time those ideals became twisted and warped, thus making him a greedy, arrogant and overconfident individual. His incarnations differs considerably: in the manga he used the Katou Organization as mere guinea pigs to show the prowess of the Thunderclap, while in the anime he initially forged an alliance with them, though his greed for power prompted him to try and subdue them as well after staging a coup d'état that granted him the control of Japan. Kiriyama was a Factor, and to crush the remains of JUDA after conquering Japan he fought them himself, though he was defeated after being publicly unmasked as a ruthless dictator and one of the stage figures of the coup. He was recovered by Katou, and thanks to Masaki Sugiwara, revived as a Machina-turned human. Being fused with his Machina made Kiriyama completely insane, and also heralded his demise when, while fighting JUDA a second time, he fused almost completely with his Machina and was obliterated, musing in his last moments on how he truly admired Reiji's old ideals and how he wanted to be a hero for him.

Eiji's Machina is Pretender, a machine most unique in that it is the only Machina that can transform, changing from a fighter jet to a walking mecha at high speed even in mid-flight. Despite its bizarre appearance it benefits from an enormous mobility and a huge degree of firepower, granted by a large number of missile launchers and wireless Nerve-Crackers identical to those used by Deceive. For close combat, it is armed with a massive combat knife.