The time is near future-Tokyo, Japan in 2040. Reito, a young man suffering from an intractable disease, vows to reunite with his childhood friend Erisa and decides to "cold sleep" to cure her illness. When he wakes up five years later, the world was undergoing a major transformation. The MK (Male Killer) virus kills 99.9% of men on the planet. The ground was a super harem with 5 billion women for every 5 men.

(Source: Crunchyroll)