I think that your little sister will be delighted by this series (if she is 13 years or so). Everything is very nice, beautiful, and represented in pink. However, this series will make older viewers frankly bored. This is a very girly and beautifully drawn anime with great soundtrack and cute characters. Kind of a "Outlaw Star" for younger ones. You can safely recommend this series to your friend's young relatives. And do not look for fan-service here, Mouretsu Space Pirates is just a naive touching anime.