Read manga: Shuumatsu No Waltz

manga
Summary:

In a world that's heading towards its end, Shirou, a scientist whose sole purpose in life is to create butterflies that can purify the world, encountered a male humanoid called Kuroe. What is Kuroe's real identity? Why does he proclaim in wanting to meet Shirou? This is an eternal love story that was born at the end of the world.