Sky Girls image - Anime Fans of modDB

Synopsis Sky Girls:
In the late 21st century, the WORMs attack the earth and destroy about 1/3 of humanity in their first wave. WORMs are huge monsters made of nanotechnology which resemble the first thing they see, usually sea organisms. After the war takes a fatal direction, humanity overcomes thier internal problems and forms a united military force to stop them. The war goes worse and as a last resort, WMDs have to be used to get rid of them. With only 10% of the people left, almost all men (why only men???) between 20 and 40 dead, the continents ripped apart and flooded, a new, uncertain era begins.

10 years later, the WORMs reappear, but a new weapon type, the Sonic Diver, has been developed to counter them. Originally 3 young girls, later 4, are the pilots of those mini-mecha/powered exosceletons and fight against the massive beasts. They have to overcome their problems with each other and become friends and trustees, because only with teamwork they can win and save the remaining people. Sometime, they learn what the WORMs REALLY are and the reveal is indeed terrifying.

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Despite the obvious fanservice (see picture), it's actually rather tame (excluding the OVA which later spawned a series). Sky Girls is mainly about action, young girls and nakama. If you like Mecha and all of the above, this series is recommended. (This is also the series which was later followed by Strike Witches)