Acronix is one of the two current (and powerless) Elemental Masters of Time. He is the younger twin brother of Krux. Once a proud Elemental Master who helped win the Serpentine War, Acronix and his brother betrayed the Elemental Masters due to them believing that their element was the strongest. In response, their former allies forged a set of weapons that absorbed the twins' elements. Acronix and Krux were lost to the Temporal Vortex, but Krux managed to escape. For forty years, Acronix remained in the vortex and didn't age during that time. Upon his return at the Monastery of Spinitzu, he was confronted by Wu, who had been waiting for him. Acronix was swiftly beaten by Wu, but by using the Forward Time Blade, Wu began to rapidly age. Acronix reunited with his brother, who had bred an army of Vermillion snakes. After capturing Cyrus Borg, they began building a time-traveling weapon, the Iron Doom, so they can travel into the past and give themselves a better future. Despite his brother's animosity towards technology, Acronix greatly enjoyed it; the siblings disagreed constantly, but nevertheless strived towards their goal together. Without a master to guide them, the Ninja fought against Acronix and Krux numerous times but were unable to gain the upper hand. Ultimately, the Iron Doom was completed, and Acronix traveled back in time to defeat the Elemental Masters. Kai and Nya made a final effort to thwart their plans by aiding the Elemental Masters. When the Iron Doom tried traveling into the future, Wu removed the Reversal Time Blade from the weapon—causing it to spiral out of control. Though Kai and Nya escaped, Acronix was lost in the Time Vortex along with his brother and their former ally.