A mage travelling with Lutecia and Agito. He is very mistrusting of Jail Scaglietti.
In episode 24, it is revealed that Zest used to be a close friend of Regius Gaiz before the latter fell under the sway of the TSA High Council. While working with Quint Nakajima and Megane Alpino in the investigation of what was known as the Combat Cyborg Incident, Zest ignored an order from Regius to back off the investigation. As a result, the three were killed by the Numbers, and Zest was used as the base for an Artificial Mage. The copy was imperfect in the form of health complications that would eventually take Zest's life, and he took the time he had to hunt down Regius, wanting to know why his team was "sacrificed". In the end, he never got his answer, as Duo took the opportunity to kill Regius - however, Zest killed Duo in revenge, and earned a knight's death at Signum's hands. His appearance may be a homage to Zengar Zombolt of Super Robot Wars.
He is named for the Honda ZEST.