Exos is the quintuplet brother of Stratos, Thermos, Tropos, and Lithos, and the brother of Terra. In his youth, Exos, out of hatred toward Stratos, attempted to kill him only to be stopped by Lithos. Exos then killed Lithos by cutting him across the chest with his knife and fled as Stratos stared back at him in rage, promising that he will never forgive Exos. Later, as he grew, Exos attacked his sister Terra and, against her wishes, pushed her off a cliff to her death in the ocean below.