Sky_Girls 01 raw
Aliens attacked Earth. Earth used ultimate weapon to wipe aliens. Earth now mostly under water.
Years later, signs of alien presence are detected again. Special ship with special new weapons goes at sea to investigate. The special new weapons are called Sakurano Otoha, Sonomiya Kren and Ichijo Eika, aka the Sky Girls.

Sci-fi mecha with barely-legal robots.

Top-notch animation, top-notch voice actors, plot... ultra-simplistic.
Killer robots that put sunscreen oil, drink orange juice and behave like giddy schoolgirls? Earth can rest assured, the alien menace will be defeated... or not.
Oh well, it's cute. ^^