"In the near future--Tokyo, Japan in 2040-- Reito, a young man suffering from an incurable disease, vows to reunite with his childhood friend Erisa and enters a ""cold sleep"" in order to cure his disease. When he wakes up five years later, the world has changed dramatically. The MK (Male Killer) virus has killed 99.9% of Earth's men. With just five men and five billion women, it has become a super harem. Only five men, known as ""numbers,"" are resistant to the MK virus. As one of them, Reito is asked to ""mate"" with the remaining women for the survival of humankind. A harem lifestyle was waiting for him in a post-pandemic world. Meanwhile, Reito is dragged into the global conspiracy surrounding the numbers. Can he overcome temptation and save the world?"
—Crunchyroll