Wu confronted an old adversary, Acronix, who would strike him with the Forward Time Blade that caused him to rapidly age. This rendered Wu unable to help his students. During a trip to the past, Wu's health is restored by Nya using the Reversal Blade, and he helps battle his old enemies, the Time Twins. During a climactic confrontation, Wu sacrificed himself to protect his students and was lost in time with the twins, leaving Lloyd in charge of the Ninja. Lloyd made the first order to find their lost mentor.
Wu went to the monastery, where he examined his pocket watch and waited as a rift opened in the sky. Acronix emerged from the Time Vortex at the ruins of the old monastery just as he was when he went into the Vortex. Upon arriving however, Wu confronted him and intended to finish their battle once and for all.
Eventually, a battle between the two broke out with Acronix confident in his ability to defeat his much older opponent. After nearly falling to his death, the Forward Time Blade lands in the center courtyard and causes time to skip a minute, ultimately saving him and allowing him to claim the weapon. With the Blade, he succeeded in accelerating Wu's growth, making him feel older. When the Ninja interfered, he defeated them with ease and headed to the Ninjago History Museum to meet someone after being assumed deceased after the Forward Time Blade supposedly was destroyed by Lloyd, Kai, and Jay.
The trio snuck on board the Iron Doom again and confronted their foes again. The outraged Time Twins fought them with Wu fighting Acronix before the latter went to aid his brother and they overwhelmed the two Ninja.
Just as they were about to kill them, Wu (who had seen Ray rapidly aging) intervened as Acronix taunted that there was nothing he can but Wu proved him wrong by quickly grabbing the Reversal Time Blade and sabotaged the Iron Doom. Wu then threw the Blade to Kai and Nya, which tossed them out of the Vortex and into the present time, as Wu stayed behind and fought The Hands of Time.
When they questioned him over the madness of his actions, Wu firmly told his foes that they will end their conflict once and for all as they continued fighting, while traveling further in the future.