(Note: This guide is provided only to identify secret achievements. I'm afraid that I couldn't answer any question about this guide.)
Kurisu made her appearance!
There are two ways to make Kurisu appear in the game.
1. Fight with her in online versus play. You don't have to win the match.
2. Finish Arcade mode with all characters. It seems that you also need to finish with the 3 extra characters - Infinity, Fin and Rimi - as well as the original 10 characters.
Clearly, the first way would be easier.
Note that to use Kurisu as a player character, you still have to unlock her.Related Achievement
(Unlocked Kurisu as a playable character)