Sigma Star Saga

Completion bonuses:
Successfully complete the game and save when prompted after the credits. The cleared game file will be marked with a gun data icon. Select the cleared saved game to play again with your old gun data intact and alternate endings.

Sigma Ship:
Successfully complete the game to get the Sigma Ship in random encounters.

Hint: Defeating the final Boss:
At the start of the game, when you manage to get to the final Boss, stay at the top of the screen and to the center. Switch to your bombs. Stay still and keep using them. The bombs will drop onto the Boss ship and blow off the pieces. If done correctly, you should get through the fight without being hit once.
Information in this section was contributed by Parasitic.

Hint: Alternate ending:
At the end of the game, instead of destroying Pysme's ship, disable it by taking out the guns instead of the eyes. She will fall down to Earth. After you kill the Overlord you will find her on Earth. When you get back to Earth instead of you being the last man on Earth, you will find Pysme down there. She will ask you to show her around Earth.
Information in this section was contributed by Yashar Golabi.