In Dynasty Warriors: Gundam 3 for the PS3 and Xbox 360, there are several alternate costumes you can unlock by complete certain missions.
Here is the list of unlockable costumes, and which missions you must complete to unlock them.
Amuro (0079) – Clear the “Escape” mission
Amuro (Z) – Clear the “Riders in the Skies – Epilogue” mission
Char (0079) – Clear the “Space Fortress A Baoa Qu” mission
Char (Normal Suit) – Clear the “Space Rainbow” mission (Neo Zeon)
Char (Z) – Clear the “Love is the Pulse of the Stars” mission
Haman (Normal Suit) – Clear the “Warriors, Again…” mission (Neo Zeon)
Haman (ZZ) – Clear the “Conviction in the Cosmos” mission (Axis)
Katejina (Long Hair) – Clear the “Ascent of Angels” mission (Zanscare)
Laura Rolla – Clear the “Moonlight Butterfly” mission
Milliardo (Zechs) – Clear the “The Final Victor” mission (White Fang)