Youjuu Kyoushitsu

One hundred million years in the past, an ecological catastrophe forced Demon Beasts to depart this world. To pave the way for an invasion force, they now require human females for breeding, aiming to produce a hybrid creature. Kayo, a nineteen-year-old woman, is assaulted by a lover under demonic possession. Interplanetary Mutual Observation Agent Muneto, also nineteen, is tasked with her protection. She gives birth to a mutant Demon Beast driven by lust, which Muneto must confront.