Appleseed: Prometheus no Shintaku is a side-scrolling shooter that's based the manga and anime Appleseed.
Sound Test#
At the title screen, hold L + R and press Left, Down, Right, Down, Left, Up, Right, Down, Left, Down, Right, Up, Down, Down, Up, Down, Right, Down, Left, Right, Down, Right, Down, Left, Right, Down, Right.
Level Select#
At the title screen, press Left, Down, Right, Down, Left, Right, Down, A, Left, Down, Right, Up, Right, Right, Down, Right, Right.
(Source: GameFAQs (real_mukimuki))
Free-Movement Mode#
At the title screen, hold L+R and press Down, Right, Down, Left, Right, Right, Down, Right, Right, B, Down, Right, Up, Left, Down, Right, Up, Right, Down, Right, Right, Down, Up, Right, Down, Left, Down, Right, Down, Left, Right, Right, Down, Right, Right. The music will stop to confirm correct entry. Start the game, pause, and press A, X, B, Y. Unpause to be able to move the player around freely with the D-Pad. Hold L+R to speed up.
(Source: Yamada_Arthur)