Figurehead

Several generations after the settlement of Milky Way. On a planet far from the galactic frontier, a boy from slums named Howell sneaks into a pirate ship landed nearby. There he finds a girl named Twin, thinking that she is a captive he decides to rescue her. While running from the pirates together, they become friends and he decides to protect her, no matter what. Unknown to him, she actually is the central part of the most powerful battleship in the universe, Zephyrus! He gets pulled into the center of a war that spans the galaxy... [Translated from Getchu]