Muyuu Senkyou Romanesque: Chronicles of Refugia

In the year 23XX, the world as we know it has come to an end.
Global warming has caused the sea levels to rise, submerging coastal cities in every nation—a mass extinction event that forever changed life on what remains of the surface.

This extreme climate change sparked violent conflicts in which android soldiers and drone strikes destroyed even more of the land. Now that the last dregs of humanity live within the confines of designated shelters, for the first time, they are forced to accept outsiders in order to secure their own safety.

You see, not everyone who looks normal on the outside is human on the inside. And while the rest of the world sleeps, these non-humans are slowly taking over…

[From the official website]