In order to help awaken Atun, Dr. Adams had Cyborg 0015 kidnap Miki Makimura so as to lure Devilman to his laboratory. Eventually, Atun fused with the body of Set/Cyborg 0018, creating a demon-cyborg hybrid. Atun's first move after gaining a new body was to kill Dr. Adams, not liking how that the scientist was trying to control him.
Atun later encountered Devilman and attacked his old rival. Around that same time, 001 and 0015 launched a wave of anti-energy at Atun and the High-Teen Number Cyborgs to disable their cell regeneration. While the wave worked on the cyborgs, it also had the affect of evolving Atun/Set into an entirely new being.
The new entity reverted back to Atun after 0015 convinced Set to leave his body. Glad to be back in his old form, Atun attacked Devilman and the 00 Cyborgs, but was eventually destroyed by the combined efforts of Devilman and Cyborg 009.