Unlockables
Unlocking Remilia, Yuyuko, Yukari, and Suika for Arcade, Duel CPU, Duel Human, and Practice Modes
To unlock any of these 4 for all non-Story Modes, simply encounter and defeat them in Story Mode. (Unsure of whether Arcade Mode works as well)
Unlocking Remilia and Yuyuko for Story Mode
To unlock Remilia and Yuyuko for Story Mode, complete Story Mode for the first 6 characters.