In 2040, Reito Mizuhara is cryogenically frozen after he contracts multiple sclerosis. Five years later, Reito is cured and revived by Mira SuÅ. Mira explains that four years ago, the Male Killer Virus emerged and wiped out the male population except for him and four other immune men who were similarly frozen and they are obligated to have children to save humanity from extinction. In disbelief, Reito goes outside and is quickly attacked by lust-crazed women until he is rescued. His sister Mahiru, who is now a teenager, arrives and explains that their brother Ryuu contracted the virus and had to be frozen to save his life...