The gameplay is just like chess, with King Neptune being the King. The player must protect King Neptune to keep from losing. Standard chess rules apply to this game, with some exceptions, such as the fact that sometimes the opposite player ("black") starts.
There are two modes: single-player and two-player. In single-player, the player must defeat a computer at chess, with different intelligence depending on the computer's level. To win the best score, as little number of moves and lost pieces must be done (though the "point rule" in chess doesn't apply here). There are five grades (is there five grades?): A, B, C, D, and F (if you lose or surrender).