Oh yeah, that would be important! I forgot to mention in the manual that you can regain 1 MP via melee attacks. Monsters will also steal 1 MP from you by meleeing you, though! Sorry about that!
Also, the water element spell will drain a larger amount of MP from an enemy, but you may or may not start with that spell; if not, you can learn it by fighting lots of slimes, because slimes have water attunement.