ZEL first introduces themselves at Obsidia Park, in front of a mass of metal and flora that has ensnared Amaria and Florinia. ZEL at first appears to be arguing with an unseen accomplice, but as the conversation continues, it is made clear that ZEL has three distinct personalities: Zero (dialogue presented as Zel), Eve (dialogue presented as zEl), and Lumi (dialogue presented as zeL).
Zero is the most aggressive personality, acting harsh to others and even their other personalities,
Eve is the smartest personality, developing PULSE machines entirely on their own, and possessing a great understanding of Pokémon's abilities.
Lumi is the kindest of the three, cheering on the Tangrowth in the PULSE Machine despite all the damage it causes, encouraging Eve, and attempting to be friendly and polite to the player.
After the defeat/death of the PULSE Tangrowth, Zero and Eve argue with each other over Zero's error in using the PULSE Tangrowth for battle, while Lumi apologizes to it for not stopping them.
ZEL is encountered again in the Beryl Ward with Taka and a mysterious agent, irritated with the player's interference. After Heather's interruption, the agent commands them to team up with Taka against the player. After their defeat, Eve gives a frank analysis of the situation and determines there is no use in their staying, and Lumi's nervousness guides the trio to follow Taka.
A diary discovered in Ametrine city reveals the history behind this odd character-ZEL truly is three people in one body, fused together as the result of a PULSE Machine attached to a Magneton that evolved into a Magnezone while it was still hooked up. Evelyn, the original identity of Eve, had developed the machine in an attempt to heal her sister, Luminia, the original identity of Lumi, hoping to keep her from dying. Zero, a member of Team Meteor, somehow learned of Evelyn's project, and attempted to force her into giving the power behind it to the organization. Luminia, sickly and frightened, simply feared death and being alone. As the great accident occurred, all three of them got what they wanted, but in a terrible manner.
After the protagonist, Victoria, DJ Arclight, Adrienn, and Ame are all captured by Team Meteor during the attempted raid on a Meteor facilty hidden in Devon Corp and transported to a hidden base elsewhere in the city, ZEL stayed behind after the base was evacuated, due to an unknown source inserting a corrupted program into the data of the PULSE that empowered the Magnezone responsible for turning them into ZEL. They are encountered a final time in the chamber containing said PULSE Magnezone, where, after questioning if the "heroes brigade" planned to destroy everything there, ZEL engages them in battle with their full team, including the PULSE Magnezone.
However, after Magnezone is defeated, Lumi and Eve are seemingly expelled from Zero's body, leaving him alone for the first time since the accident and horrified by the loss of his comrades.
Zero immediately leaves for Agate City afterwards.
The types of the three Eeveelutions ZEL uses in battle reflects their personalities-Ice, being rather frail, matches with Lumi, Psychic, relating to the mind, matches with Eve, and Dark matches with Zero's more cruel personality.