MuvLuv Unlimited

Based on the game by Age, sequel to the original MuvLuv game, taking place in an alternate universe where the Earth is invaded by aliens.

From Animaxis:
One day boarding school student Takeshi awakes to find himself in another world, one threatened by mysterious invaders. He soon learns that his only chance of returning home is to join forces with a group of beautiful female warriors, most of them mirror images of classmates and friends