Mermaids are a marine race appearing in the original Final Fantasy. They have humanoid upper bodies, but have fish-like lower bodies. They inhabit the Sunken Shrine near Onrac and the Lifespring Grotto. When the Warriors of Light arrive, the Mermaids ask them to destroy Kraken for them. The heroes succeed, and the Mermaids' existence is no longer threatened.
It's been said that mermaids lived with their human companion in Lifespring Grotto, but inside the dungeon you can only find mermaids who are often salvaging tinkers from water.