To get every illustration, do as follows:
- Complete all Story Mode paths.
- Complete Arcade Mode using every character. (Beginner difficulty with 1 round is fine, and you do not have to reach Order Sol.)
- Complete EX Arcade Mode with every EX character. (Hold LT when picking Arcade from the main menu, press Start when selecting a character.)
- Complete Survival Mode.
- Get to at least level 500 in Classic Survival Mode. (Hold LB when picking Survival on the main menu.)
- Complete every Mission with every character.
- Get a "GGXX" rank on every Mission.
For Mission Mode, the game's difficulty does matter. In fact, you cannot get a GGXX rank on anything less than Maniac difficulty. Note that you only need to get a GGXX rank for one character each mission. All other characters are free to beat that mission on Beginner difficulty.