Various parallel worlds, including those of past Super Sentai, were sealed into Toziru Gears by the Tozitend Dynasty of the parallel world of Kikaitopia. The final world in their sights was the one where Kaito Goshikida resides, but it was fused with a portion of Kikaitopia. A month later, the Kikanoids managed to integrate with human society, but the Tozitend launch an invasion, creating a massive rift in the unified society. While taking cover, Kaito accidentally activated his robotic bird-like companion, Secchan, who dragged him and Kaito's grandmother, Yatsude, to a secret lab created by Kaito's missing scientist parents and unveils the Geartlinger and Sentai Gears based on the past Super Sentai's worlds. Using the devices, Kaito enlists a heroic Kikainoid named Juran as they transform into the Zenkaigers and destroy the invading forces of Tozitend's field commander, Barashitara. After the battle, Kaito, Juran, and Yatsude discover the entire city and its population are sprouting mushrooms.
Realizing how the Zenkaigers could threaten Tozitend's conquest, the latter's technical officer Ijirude transforms a Kudakk foot soldier into the monster Kinoko World using the Kinokotopia Toziru Gear. Kinoko World sprouts mushrooms across the city before Kaito and Juran confront him, though he manages to escape. At Secchan's suggestion, the Zenkaigers decide to recruit others to their cause. They find little success until they cross paths with the animal-loving Kikainoid Gaon. After Kinoko World starts using poisonous mushrooms, Gaon joins Kaito and Juran to stop the monster. They succeed, but Tozitend deploy a giant Kudaitest foot soldier and empower it with Kinoko World's Toziru Gear. Juran and Gaon enlarge to fight the giant, with Kaito fusing them into the mecha Zenkaioh so they can destroy it and free Kinokotopia. After introducing Gaon to Yatsude, Secchan demands the Zenkaigers find more recruits.
The Zenkaigers keep looking for new members and encounter the female Kikainoid Magine while facing a monster that freezes everything around him.
Kaito and his friends meet the Kikainoid fugitive Vroon, who defects from Tozitend to join them as their fifth member. Now with the team complete, the Zenkaigers fight a monster who forces citizens to fight each other.
After Vroon makes an off-hand remark about Kaito's missing parents, the latter theorizes they might be prisoners of Tozitend. However, he also starts to feel guilty over not being able to help the people he had the chance to, but did not. Even worse, Tozitend's new monster, Sushi World, traps Kaito and Juran in a giant sushi roll. The remaining Zenkaigers attempt to help their comrades, but must contend with Barashitara first.
Tozitend sends a monster called Garbage World to bury the city in trash, but their former janitor Vroon leads the Zenkaigers in combating this new menace. All the while, a mysterious purple-clad individual monitors the heroes' progress.
The mysterious individual reveals himself as Stacey, Barashitara's son, and confronts the Zenkaigers directly. Armed with his own version of the heroes' equipment, he transforms into Stacaesar and uses the powers of their Super Sentai predecessors and their mecha against them. All the while, Gaon struggles to determine whether the human-like Stacey really is human or a Kikainoid.
Just as suddenly as Stacaesar's summoned Sentai appeared, they disappear just as Barashitara arrives on the battlefield with Door World to celebrate his son's first battle. The World uses their power to scatter the Zenkaigers, who desperately attempt to find their way back home. They eventually confront Stacaesar once more, during which another new individual joins the fray.
The second new individual introduces himself as the World Pirate Zocks Goldtsuiker, aka Twokaiser. He has arrived with his younger sister, Flint, and younger twin robot brothers, Cutanner and Ricky, to find the best kashiwa mochi in the universe. While in pursuit of this goal, Zocks ends up clashing with Kaito as well as Tozitend.
The Zenkaigers manage to reach a truce with the World Pirates and convince them not to commit any acts of piracy. However, a strangely cheerful Zocks continues to endanger civilians while fighting Tozitend. Wanting to find out more about them, Kaito boards the pirates' headquarters, the Battleship CrocoDaiOh.
The Zenkaigers and World Pirates find themselves in a strange game of "oni tag", wherein people designated as "oni" can turn others into more oni by touching them. In response, Zocks vows to protect Flint, who is busy trying to create a new power for him.
As the Zenkaigers and World Pirates fight another of Tozitend's monsters, Ijirude puts the final touches on Stacaesar's own personal mecha before Stacey uses it against Tozitend's enemies.
The Zenkaigers start to become popular with their fellow citizens, with Gaon in particular getting to enjoy playing with children. However, Tozitend's latest monster turns humans into Kudakks and Kudakks into past monsters the Zenkaigers previously destroyed.
Complete episode guide for Kikai Sentai Zenkaiger with detailed information about every season and episode including air dates, summaries, ratings, and streaming availability in United States.
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