Saihate no Diasta

In the far future, there exists a vast region of space that is yet to be explored called the New Space. The levels of new discoveries and dangers are unknown. The Dian sisters, Reina and Rio, made a promise to each other that they will one day journey into New Space together. The two sisters were separated and Reina became a pilot of the commercial luxury cruise liner spaceship Folshion. Rio is a tomboy who seems to have no self consciousness that she is a girl and who finally finds her sister. Rio is allowed to stay on the Folshion granted she finds herself a role on the ship. Sisters united once again, begin dreaming about the adventure into the new territory.

(Source: MangaHelpers)