Spectral Force 3

To recruit Al, you need to complete the mission "The Battle God".

Mission requirements: The Nameless Army must be destroyed, but both the Underworld Army and the Overlord Army must still survive.

Recruitment requirements: Neither Al nor Wave retreats.

Once you have unlocked the mission, simply complete it without Al or Wave retreating. Both will be present from the beginning and will actually help you out quite a bit. This mission can be a bit tricky as there is very, very little room to manuever on the map. There will also be a LOT of enemies at one time coming from both sides of your party. Make your way to Al and Wave as quickly as possible and make your stand around the Boost Point (HP). Be aware that Golbeliath (the enemy leader) will turn into a very large dragon after a few turns with a very powerful area attack that will hit your whole party.

The achievement will unlock after you have saved your game.