[Silence for a moment. No one has ever asked this, so she has to put together an answer.]

They come in many different shapes and sizes; some look relatively human, others can appear as dragons or other creatures. Their magic varies greatly, too. One called Leviathan knew water magic, for example. He's one of those that appeared as a dragon. People can learn magic from Espers, even summon them.

...well, not here.