Mini-game
At the main menu, highlight the "Options" selection and press A + X to start a mini-game.
Multiple endings
There are a total of three ending in the game. One if you save all friends, another for saving just one friend, and a third for saving no friends.
Eriko in her underwear
Start a game and do not rescue anyone. Eriko will lose more clothing with each lost friend. By the time you reach Level 6, Eriko should be in nothing but her underwear.