(Note: This guide is provided only to identify secret achievements. I'm afraid that I couldn't answer any question about this guide.)
Unlocked Rimi as a playable character.
To unlock her, you must first make her appear in the game. See the guides for the following achievement for that.
After she made her appearance, you must satisfy two of the following three conditions while playing Arcade mode.
1. No continues.
2. Win with SP super-move.
3. Cumulative total of 100 cancel out within that playthrough.
Note that you have to satisfy exactly two
of these conditions. If you satisfied that, Rimi will break into the play. Then by defeating her, you can unlock her and this achievement.