Can you name this Anime?

Ok atleast 7 or 8 years back I got into an anime that my cable provider had on demand I watched the first 10 episodes and then cable dropped it. I do not remember the name now, but would really like to start watching it again, so i am going to give a brief of what I remember of the plot line.

A teenage boy breaks into a castle where his sister worked. He had not heared from her in a long time. Over a year (i think) He is cought by teenage girls. The girls are actually piolets that man these machines that battle aliens (once again i think) The sister was one too before she went missing. the girls dont know what happened to her. There is alos a shy boy piolet. who has not had to much exposer to the outside world.

Sorry it is not to much to go on but I am hoping that an anime fan out there might know this anime.