Jun Konomaki

Akira is just another normal kid in modern-day Tokyo, until an old friend of his, Ryo, shows up and turns his world upside down. Akira learns that there is an upcoming war of demons on humanity and he has just been enlisted for a major tour of duty. But the only way to fight a demon is with their power, so Akira and Ryo risk a dangerous ceremony in an attempt to create humanity's only hope: the powerful Devilman. (Amazon)

Demons exist and their power is beyond what humans can fathom. In fact they are so strong that humans do not stand a chance against them in a fight. The only thing strong enough to defeat a demon is another demon and it is trough this logic that Ryo Asuka hatches the plan to have his good-hearted friend Akira Fudo possessed by a demon. If a person is of pure of heart then he might be able to control the demon that posses him and thereby acquire power equal to a demon. (animenewsnetwork.com)

Various characters from Go Nagai works including Devil Man, Mazinger, and Violence Jack, become trapped in a parody world where they all become super deformed. They get trapped in this mishmash, fighting each other, and are trying to figure a way back to their own world.