Unlockables for Beating the Game
You must save your game at the end of the game's credits for it to count as a completion. Unless specified otherwise, it doesn't matter which story you clear to unlock these features. Next New Game allows you to start a new game with all experience, skills, parts, and money from your preivous game. The difficulties multiply enemy HP by the stated amounts.
Buren Wanzer for the OCU story: Beat the OCU story for the first time
Next New Game: Beat the game once
Sound Test: Beat the game once
TCK Assault Wanzer for the USN story: Beat the USN story for the first time
x0.5 (overrides x0.8) and x1.5 difficulties: Beat the game twice
x0.8 and x1.2 difficulties: Beat the game once
x10.0 difficulty: Beat the game five times
x2.0 difficulty: Beat the game three times
x5.0 difficulty: Beat the game four times