Under each character's portrait there is a blue gauge that will gradually fill up as you fight and defeat enemies. The gauge is split in to three section and in order to activate an Ecstasy Combination at least one of them needs to be filled. The more sections that are filled the longer the Ecstasy Combination attack will last.
You can activate a character's Ecstasy Combination attack by pressing
and
at the same time.
If your character is in their transformed state (Dare Drive or Xtasy) this gauge will fill automatically. This gauge will also fill quicker with successful COOL combination attacks.
In order to unlock this trophy you need to built the Ecstasy guage for either Aya or Saki and activate any of their Ecstasy Combination abilities 100 times. This should come naturally as you play the game (as long as you use the Ecstasy Combination attacks of course
).