I got the Loremaster achievement on my latest playthrough, but I'm not exactly sure what unlocked it. The description says:
Research each aspect of the Moon Goddess
What exactly is this referring to? It was my fifth playthrough, and at that point I had played each of the first four classes (and the Snowdancer), and started from each village once. That said, I might have done other things for all 4 (?) aspects of the Moon Goddess for the first time, like looked at the statues in the villages or something. So I can't really tell what unlocked it.