Katsuo is the captain of the Moonlight SY-3 spaceship, and in 1999, is stationed on the moon. His role in the film begins when he calls his sister at Monsterland, but the line goes dead. Shortly after, they see an Unidentified Flying Object outside, but they decide to land at the Moon-base instead of pursuing it. When they return to the base, they are ordered to return to earth immediately and check on the base beneath Monsterland. They find the base deserted except for Kyoko Yamabe and her employer Dr. Otani. They reveal that they have been expecting the Moon party, and show them footage of the destruction being wrought on the surface by a brace of monsters. Katsuo and his crew are then introduced to the Kilaak Queen. She reveals her plan to destroy the earth civilization to build a new one, and Katsuo tries to shoot her. She then sets guards after the Moonlight crew, but they manage to kill some of them and escape. Later on, Katsuo and a doctor are seen interrogating Dr. Otani, who refuses to speak and eventually leaps from the high-rise window to his death on the beach below. Katsuo is present for the autopsy on Otani, which reveals that he was being controlled with a small sphere implanted behind his ear. It is then deduced that the Kilaaks are controlling the MOnsters the same way, and they search the globe for the other transmitters. Katsuo and the Military discuss how the Kilaaks built a new secret base while they were searching for transmitters, but at that time Kyoko comes into the room, and asks to stay there or the Kilaaks will destroy them all. Katsuo then tears through his sister's earlobes to remove her earrings which were Kilaak transmitters. Kyoko does not remember where the Kilaak base is, so Katsuo and the Moonlight SY-3 crew are called on to locate it. The SY-3 follows a Kilaak ship toward Mt. Fuji, where they find mysterious rocks with worm-like creatures in them. Katsuo deduces that this is the true form of the Kilaaks, and that they must go into stasis to live outside of volcanic climates. Seeper in the cave, the group finds a Kilaak device that they spend so much time trying to disable, that the military proclaims their mission a failure due to a lack of response. Katsuo and the SY-3 eventually return, but find themselves pitted against a mysterious monster called the Flame Dragon. They battle it for a while before learning that it is just a Kilaak spaceship, which they destroy.