Ara Fell: Enhanced Edition

There are a total of 19 Relics to find in the game. These provide permanent buffs to the entire party, so they are very useful to have. You can sell them for a nice amount of coin if you want, but I don't see any benefit to that. Money is plentiful toward the end of the game, where the buffs are more helpful. I do not think selling them voids the achievement, but I can't confirm, so that's another reason to avoid selling them.

A full list of the Relics and their locations can be found HERE, and they are again pointed out in the walkthrough I linked in the Road Map.