|This article is about a/an kaijin in Kamen Rider, the original series.|
Noboru Kusaka (草鹿昇 Kusaka Noboru) was a pro-wrestler who was modified by Shocker into the second Phirasaurus Human (人間ピラザウルス Ningen Pirazaurusu, 16), also simply known as Phirasaurus (ピラザウルス Pirazaurusu) after the prehistoric creature he was modeled on, becoming a piranha-dinosaur Shocker cyborg.
Following the death of the first Phirasaurus who sucuumbed to his own "Death Fog" during his test run, Shocker commander Maya (マヤ Maya) quickly looked for a stronger person to be altered. Kusaka was captured, brainwashed and had his body altered, becoming the perfect Phirasaurus. The new Phirasaurus was able to match and defeat Kamen Rider #2 with his Ultra Kick. Brainwashed, Kusaka returned to the wrestling world as Satan Mask, sporting a red lucha libre wrestling mask similar to the Shocker Combatmen. He attacked his own little brother, Kiyoshi when he tried to speak with him. He eventually faced Rider #2 in a wrestling ring. During the battle, he accidentally killed his commander Maya with his poisonous gas. In the end, Kamen Rider #2 and Phirasaurus exchanged a Rider Kick and a Ultra Punch. Afterwards, both fell on the ring, and Kusaka returned to human form, recovering his memories and reuniting with his brother.
The Phirasaurus Human's main ability, engineered from the prehistoric Phirasaurus, was releasing a poisonous breath. Appearing as a powerful mist, the Phirasaurus' poison was said to be able to kill a dinosaur in seconds. During its test run, the poison of the first Phirasaurus Human was able to kill a bus full of humans, however, the poison was so potent it resulted in the Phirasaurus Human dying immediately after, thus a stronger human, Kusaka, was needed to be modified. As the second Phirasaurus, Kusaka had an unbelievably strong body, able to shrug off rounds of a cannon, and special techniques called Ultra Punch and Ultra Kick, similar to the Rider Punch and Rider Kick.