The currency is munny. [Sounds similar enough to 'money' really, but her home city's currency are yuans. A gold and blue sphere is briefly lifted into view of the camera.]

The nightmares tend to drop them once they're destroyed - if you fight a lot of them, you won't find it difficult to stay in pocket. They also drop little dream pieces, a bit like the ones given by the moogles.

Apparently, it's possible to make more. There are a few people here with more than one companion.