Spectral Force 3

To recruit Chic, you need to complete the mission "Gun Obsession".

Mission requirements: Attain the rank of Gale Star, recruit both Shamazwei and Fuya, and have at least one of their guns maxed out.
Recruitment requirements: Chic does not retreat.

Once you have unlocked the mission, simply complete it without Chic retreating. Your party starts out scattered all over the map, so have them meet up where Chic is right away. Be sure to have either Shamazwei or Fuya (whichever has the maxed out gun) approach Chic to trigger a conversation. Chic will be present from the beginning and will actually help you out quite a bit. He does tend to run off on his own, however, so stay with him and heal him when needed.

The achievement will not unlock until you save your game.