If you use all your credits in Arcade Mode and fail to finish the game in your first try, you will be awarded an additional credit after the game ends.
Finish the Final Chapter in mission mode to unlock a Magnum in story mode.
Get an S rank in all the bonus training missions to unlock a shotgun in story mode.
To unlock Chapters 2-6 in Mission Mode, clear the following corresponding chapters in Story Mode:
Chapter 2-clear Guren chapter
Chapter 3-clear Gunjo chapter
Chapter 4-clear Aoi chapter
Chapter 5-clear Arcade mode
Final Chapter-clear Chapters 1-5