One hundred million years ago, an ecological disaster drove the Demon Beasts from our world. Now, they must breed with human females to create a new, hybrid creature, who will clear the way for an invading horde. When Kayo is assaulted by a possessed lover, it's up to Interplanetary Mutual Observation Agent Muneto to save her from the terrifying creature to which she gives birth: a mutant, lust-driven Demon Beast!