''Sayōnara. Yoshito''

—Kiryu's Cockpit Computer (Tokyo SOS)

Built around the skeletal remains of the Godzilla that attacked Tokyo in 1954, Kiryu was an advanced cyborg designed to defend Japan from the kaiju that frequently menace it, particularly the current Godzilla. Kiryu first saw action in 2003 when he was deployed to battle Godzilla when he surfaced at Hakkeijima. However, Godzilla's roar awakened the original Godzilla's restless spirit that was attached to Kiryu's skeleton, causing the machine to go berserk. Kiryu was recalled and his programming altered so this incident could never happen again, then was sent out against Godzilla a second time when he landed at Shinagawa. Kiryu fought Godzilla to a draw, leaving him with a gruesome chest wound and himself losing an arm. Kiryu was rebuilt over the course of a year, and sent into combat with Godzilla again when he reappeared in Tokyo. Kiryu fought alongside Mothra and her twin larvae, and finally triumphed against his organic counterpart by reopening the wound on Godzilla's chest. The original Godzilla's spirit took control of Kiryu once again and chose to sink himself in the Japan Trench with the immobilized Godzilla and deactivate himself rather than kill another member of his kind.