By now you likely figured this out, that you can't. That is just a move that you will learn at that level (after compleating certain requirements) unless you have the opposite sides Move
I.E
Fierce Demon Fang - Double Demon Fang
If you have Double Demon Fang, you can't learn Fierce Demon Fang.
Chat with our AI personalities
1st you have to have the unison attack, then put 2 or more certain techniques together, for example, with Genis and Raine, Genis use Ground Dasher then immediately use Raine's Ray then it will make Prism Stars.
By starting the "Fairy Tales Pt. 2" quest
Use the walkthrough.
You don't
you use a blue flute to wake it up.after its awake you battle it.