When Ryudo, Elena and Roan encounter Mareg along the way to Granas Cathedral, he initially mistakes Ryudo for someone else who attacked his village and attacks the party in a blind rage. Later on, the party meets up with Mareg again and after some formal introductions, Mareg joins. He explains the reason for the attack was vengeance on the demon-man Melfice who attacked his village of Nanan, and that the smell of Ryudo is nearly identical to the smell of Melfice. This, it is learned, is because Ryudo and Melfice are brothers. Physically impressive, wielding a huge halberd and possessing great height, he's also the philosopher of the party, reminding everyone of possible dangers, risks and counteractions. His tribe also has an extremely keen sense of smell, allowing Mareg to smell some things miles away. He is usually calm, passive and open-minded, though his lust for vengeance brings out the worst of him at times.
Mareg has amazing attack and defense and can wipe out enemies quickly. However, his magic defence is very low. His moves include Beast-Fang Cut, Beast-King Smash, Beast-King Blast, and Lion's Roar. He attacks using a poleaxe.
Mareg leaves the party near the end of the game, as he valiantly gives his life to help the party escape from Valmar's Moon.