Rerasu was a massive but thin demon that stood several feet high. He had eagle like features with a large blue beak and green feathers around his head and chest. He had banded arms and legs, giving him somewhat plant like features.
Devilman, Daruni, and Rerasu were the bodyguards of the great demon Zennon. They were summoned by Zennon to lead the attack against the human race.
When Akira Fudo and his father Professor Fudo clumsily fall down a large crack in the ice whilst exploring the Himalayas; they encounter Zennon the leader of the Demon Tribe who promptly kills the both of them.
Zennon then calls out Daruni, Devilman, and Rerasu and commands them to battle to the death over the body of Akira Fudo so they can lead the attack against the human race. Rerasu tries to take on Devilman but is quickly knocked down to the floor. While Devilman fights against Daruni, Rerasu breaks off an icicle hanging from the ceiling of the ice cave and tries to stab Devilman in the back. But Rerasu is knocked back by Devilman's wings were he falls and stabs himself in the eye with the icicle, killing him.