Summary from PC version:
Popular Japanese video game series produced by Koei as part of its rekoeition games. In East Asia, the series has a large cult following, but has not received much recognition outside East Asia. The series has been compared to Sid Meier's Pirates! in gameplay and theme. It is a simulation and CRPG series dealing with sailing and trading.
In the games, the player takes up the role of a captain (also called commodore in some translations) and manages a seagoing fleet to participate in trades, privateering, treasure hunting, exploration, and plain piracy. Even though the series is largely open-ended, there is still a loose plot which requires the player to follow certain paths, and deviating from these paths may stall the progress of the story.