The "Abductors" Invaders from Altea come to Earth with only one purpose, to harvest humans. DEAVA the Aquaria Academy exists to train men and women to use Aquaria, but they cannot ever merge because of Guize stones, these block an "unholy union" between genders. The story follows Amata and Mikono in their enrollment into DEAVA, and fight their fight with Abductors.
(Source: FUNimation)
— Description from AniList community (anilist.co).
