Zenos never was a normal child. He was the imperial heir, and thus was he expected to learn close to anything, from history and literature to war strategies to the art of combat. He has always had strict tutors and teachers. His mother died when he was still a child, and he seldom ever met his father, who sent him servants to use and command as he pleased instead. For this reason, to him the servants and tutors were worth close to nothing, and more similar to magitek equipment than to people. He had no children of his age to play with, and even the servants kept their distance due to fear of him. He had always been brilliant and outstanding, especially in combat, but for his father it was never enough.

At the age of 14, he was taught swordsmanship by an eastern swordsmaster, whose true aim was to kill Varis, the Emperor. Zenos found an enemy he could not beat for the first time, and studied him until he understood his technique, called the Unyielding Blade. Once understood, he replicated it: he forced his own body to release aether with the use of a crystal, and as the teacher attempted to kill him, Zenos murdered him instead. Ever since, he has never again found a worthy opponent.

Growing up, he became the Legatus of the XIIth imperial legion and conquered the city of Doma, becoming his regent soon after. He had no interest in ruling, though, so he soon after found use for a local woman, Yotsuyu: after Gaius' defeat at Praetorium, Zenos was named viceroy of Ala Mhigo,  and he named Yotsuyu as Doma's viceroy to make her crush her people's will in his stead. He then heard from Gaius' reports of the Echo, a very special ability that the Warrior of Light possessed, and thus did he recruit Aulus to research it. There were two main test subjects for his experiments: Grynewaht, who ended in failure and madness, and Fordola, who was instead mostly a success and helped perfect the process. Zenos then underwent the experiment himself and gained a power called Resonance, similar to the Echo, that let him use magic at will and possess other people's bodies. 

After his fight with the Warrior of Light in Ala Mhigo, he was thought to be dead, but he instead found out of this ability: possessing the body of a soldier, he fought his way back to his own, which was possessed by the Ascian Elidibus. He took his own body back, along with information on the Warrior of Light, and killed his father Varis, who had tried to kill the Warrior. He had no interest in the throne, though, so when the civil war started and the potential heirs were killing each other, he simply watched in boredom. He was eventually approached and convinced by Fandaniel to take it himself - it was the perfect spot to pursue both of their plans: the power of Zodiark for Zenos, and the Final Days for Fandaniel. Zenos and Fandaniel had the imperial palace rebuilt into a tower, which hid the means of teleportation to the moon, where Zodiark resided.

Zenos went to greath lenghts to make the Warrior want to fight him, even kidnapping him and stealing his body to murder his friends, but he was stopped by Fandaniel and the arrival of the WoL. Soon after, Fandaniel betrayed Zenos: they both traveled to the moon, but the Ascian took Zodiark for himself, and was defeated by the WoL. Zenos realized that his "friend" would not concentrate on him until the final days were stopped, and thus chose to wait, keeping himself busy outside of Garlemald, because he was stripped of his title and dubbed a traitor, "viator" by his people.

After the death of Fandaniel and Zodiark, the Final Days started and the Warrior focused on preventing the end of the world. Zenos took the time to think of wat he truly wanted from his "friend", so he eventually chose to help them. He traveled to Old Sharlayan and offered to help in the form of Shinryu in exchange for the Mothercrystal's aether. He stood to his word, helping the WoL defeat the Endsinger, and after that battle he asked for one, final battle. With nothing to hold the Warrior back, Zenos finally found acceptance, and the two fought to the death.