Namine tilted her head to one side for a moment as she thought. "I think Fire."

Possibly due to her improved relationship with Axel before arriving in the Realm of Sleep, and Lea having been here for a while, she had a greater affinity for it. Mostly her problem was in actually using on Nightmares. Focusing too hard on trying to cast the spell and visualizing something burning did bring up unpleasant mental images more often than not.