Complete the following tasks for each character in Official mode to unlock the corresponding alternate movie ending at the "Gallery" menu.

Amuro (Encounters in Space): Do not let Kai or Hayato to be defeated.
Amuro (Escape): Allow Kai and Hayato to be defeated before completing the mission.
Char (At the End of the Battle): Let Kamille talk to Scirocco before defeating him.
Char (Prelude to Counterattack): Defeat Scirocco before Kamille talks to him.
Judau (A New Journey): Defeat Haman after their conversation ends.
Judau (Meeting Again): Defeat Haman before their conversation ends.
Kamille (Love is the Pulse of the Stars): Save Radish from Yazan, save Emma from Reccoa, and allow Colony Laser to fire.