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.
When the Ninja bombarded Wu with questions about Acronix, he told the Ninja about the Time Twins.
During his youth, the Elemental Alliance would fight the Serpentine. Shortly after, the Time Twins betrayed them, and they had to fight back with Time Blades forged by Ray and Maya. After stripping them of their powers, they sent the Blades into a temporal vortex.
Misako told the Ninja that Wu needed to rest, so they left him alone.
When the Ninja went to see Wu, he was too tired to answer their questions. Later, Lloyd asks him what a Master must do, but he kept falling asleep before he could tell him.
Wu wakes up from a nightmare, with Misako next to him. He confessed he was hit with the Time Punch and told her not to tell the Ninja.
Later, he told Lloyd that he wanted the whole team to be there at the fight with Acronix, not just Lloyd.
As Lloyd tells Wu about the Ninjas' previous mission, he was sleeping. Later, when he woke up, he saw the Ninja playing with the Blade and told them not to do so.
A moment later, they were attacked by Vermillion. He sat next to the Time Blade in order to build his strength. Eventually, he was almost attacked by a Vermillion and Acronix.
When the Ninja were slowed down, the twins took him with them.
When Wu was brought into the Vermillion Dome of Doom, he commented how the Vermillion Army's celebration is premature.
Wu fought the Vermillion, stating his strength has returned. He then sees Misako, who said he failed her. His other allies did the same, but this turned out to be a hallucination and Wu is still tied up in a cell guarded by Blunck and Raggmunk. When Lloyd came to save him, Raggmunk took Wu away from him. When Lloyd defeated Raggmunk, he was headed toward a cliff. Lloyd was able to save him, but he was kidnapped again.
In a flashback, Ray explained that Wu requested them to forge the Time Blades to defeat the twins. Just when the twins went into the vortex, Wu saw a clue that Acronix would return forty years later.
In present time, Machia shows Wu to Kai, Nya, and their parents. Acronix explains that the only way to undo the Time Punch is with the Reversal Blade.
Wu waits on the airship for Kai and Nya to return with the Reversal Blade to save him. Once they did, the twins stopped them and let them fall into the Boiling Sea. They were saved when Kai and Nya summoned the Fusion Dragon. When they let them fall into the Boiling Sea, Nya and Kai used the Fusion Dragon to save everyone.
They followed Iron Doom into the Temporal Vortex, with Ray and Maya jumping off to increase speed.
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.