Hurrah! Sailor (2004)

Blurb:
Sometimes in life, we have to stop what we’re doing to ask ourselves, "why does it have to be like this?" The world of Katsuo Nakane’s, Hurrah Sailor, deals with this question as Konika, Ichino, Mareta, Shoya, and Ensign Kurie find themselves stranded on a planet whose inhabitants have developed virtually no technology at all.

The Two United Empires and the Federation Kingdom have been at war for centuries and entire galaxies have been turned into war zones. With neither side ever achieving a decisive victory, the conflict has been dragging on so long that both sides have even forgotten the reason why the war originally started.

But now, for Konika of the Federation Kingdom, and the others from the United Empire, they must put aside their differences to find a way off the planet together. In the process they find that perhaps there are no differences between them and some of them begin to wonder if they wouldn’t be better off not returning to the war.

Source: www.anisearch.com/manga/5104