Tachibana continues to train Mutsuki to overcome the Spider Undead. A friend of the Kurihara family, Kamioka, takes Aikawa on a photo shoot. Garren and Leangle try to seal the Mole Undead, but Mutsuki loses control again and is dragged underground. While on the job at the zoo, Aikawa is attacked by the Orchid Undead. The Eagle Undead arrives and drives the Orchid Undead away. While Mutsuki tries to find a reason to face and seal the Undead, Blade and Garren become overwhelmed by the Mole Undead.

Mutsuki overcomes his fear and seals the Mole Undead. Kamioka begins questioning Aikawa's presence at the Kurihara house. The Eagle Undead kidnaps her to trap Aikawa and steals his Change Card. Blade arrives and sees Aikawa transform into the Dragonfly Undead. The Orchid Undead attacks Mutsuki but flees. Blade retrieves Aikawa's Change Card from the Eagle Undead and seals him. Kamioka discovers Aikawa's secret but now believes in his goodness.

The Wolf Undead is changing people into werewolves. While fighting them at an amusement park, Leangle meets a group of human Undead Hunters. Leangle, Blade, and Garren encounter the Wolf, Orchid, and Elephant Undead, but they all escape. The Undead Hunters meet with Kenzaki and Garren to discuss an alliance. They help the Hunters complete a new bike, Black Fang.

The Wolf Undead steals Black Fang as Garren and Blade try to retrieve it. Chalice chases after the Orchid Undead, but Shirai finds her and heals her wound. Kenzaki and Tachibana find Shinmei, the leader of the Hunter, and discover that he is the Wolf Undead, so they chase him to the docks and seal him. Chalice finds the Orchid Undead and seals her.

While terrorizing people, Leangle is photographed by King, the Caucasus Undead in human guise. Kenzaki asks Aikawa to join them, but Tachibana does not trust him. King creates a website to slander the Kamen Riders and everyone seeks him out. Kenzaki encounters King, but has his Blay Buckle stolen by the Scarab Undead, who can stop time. Tachibana finds Mutsuki in a bar and learns of Aikawa true identity as the Joker Undead. Kenzaki retrieves his Blay Buckle, but Aikawa is abducted by the two other Undead. Kenzaki then encounters Trial D, an Undead that cannot be sealed.

Garren arrives to assist Blade and drives off the new Undead. Tachibana tells everyone about Aikawa's identity as the Joker Undead. Meanwhile, King holds Aikawa and forces him to transform into his Joker form, which he uses to escape. Tachibana meets Hirose's father, who is behind the Trials. Kenzaki finds Aikawa and learns about how he changed from the Joker Undead to Hajime Aikawa. King and the Scarab Undead appear and fight Blade. Aikawa helps Blade seal the Scarab Undead while King flees.

Blade and Garren fight over what should be done about Aikawa. Hirose's father contacts Tachibana and shows him the Trials. The Kenzaki encounters King and learns that Aikawa needs his cards to prevent his transformation into Joker form. Kenzaki is defeated and later ambushed by Trial D.

Kenzaki realised what was Trial D's motive. He decided to leave town to avoid further harm to other people. Mutsuki battled Hajime into a battle but was attacked by his Fusion Wolf form instead. King also gave Mutsuki Chalice's cards. King was surprised that his popularity grew but was interfered by Blade instead. Blade finally sealed his final deck card, Evolution Caucasus. He also managed to fuse into King Form and destroyed Trial D with Royal Straight Flush.

Another Trial Undead is hot on Kenzaki's trail, he can also use Kenzaki's moves! Meanwhile, Hajime can no longer control himself and fights assuming his Joker form.

Hajime has been taken over by his Joker form. No longer in control of himself, he cannot see the differences from humans and Undead and it's Kenzaki's King form to blame.

In order to get back Hajime from his Joker form, Kenzaki asks Mutsuki to give him the 5 cards of the Chalice deck that are in Mutsuki's hands, but for that he must let Mutsuki have his Rouze Absorber. Kenzaki makes the deal and with Tachibana, obtains the King of Hearts card. Hajime uses the card to finally suppress the Joker form and defeat the Trial.

Hajime's problem was solved as he can turn back into a human, but the new problem is on Kenzaki as he and Mutsuki have been tricked by Hirose to fight each other, and Leangle forces Blade to change into King Form. But he knows the King Form is fighting like crazy, but then Chalice comes with the Wild Form and suppresses the power of Blade's King Form.

Mutsuki wishes that he will be the strongest Rider by fighting against the Tiger Undead but loses instead. But while confronting the Giraffa Undead, the Tiger Undead learns the truth behind the "Battle Fight" before facing Tennoji and his creation: The Titan.

After being poisoned by the venom of the Scorpion Undead, one of the two Undead fused into the Titan. Mutsuki attacks his friends and turns into the Category Ace. Everyone is not spared even his girlfriend, Nozomi. The Tiger Undead has already been sealed and Mutsuki is forcing himself to fight Blade in his King Form. Will the transformation be complete or a failure?

New Undead are born, and its identified as a fifth ace Keroberos, now all 4 Riders must face this powerful new Undead.

Though Keroberos was sealed, Tennoji reveals his true plan as he fuses with the sealed Undead to become all powerful. However, once Tennoji is defeated, the Giraffa Undead murders him and takes the Keroberos card, allowing the true Battle Fight to begin.

There are only two Undead left and if it's up to Garren, the Joker goes first, but in the heat of battle, will he change his mind or die trying?

With Garren out of the game and Hajime declared the winner, Blade and Leangle are the world's last hope, to seal the Joker. However, they have to deal with the endless army of Dark Roaches that are systematically destroying the human race.

Kenzaki confronts Hajime in an all out battle with the human race's existence on the line. But can Blade manage to save the world on his own or does the Joker have a plan that will negate the Battle Fight's end game?

After Natsumi Hikari has a nightmare of every Kamen Rider being defeated by a figure called Decade, she helps her grandfather Eijiro deal with unsatisfied customers. The photographer, Tsukasa Kadoya, seems to be at fault, but he simply tells Natsumi the photos are bad because he does not belong in this world. After the argument, various holes in reality open, allowing the Orphnoch, Undead, Makamou, Worms, Imagin, and Fangires to start terrorizing their world. In the bedlam, she finds a corroded belt and book, recalling it as Decade's from her dream. She gives Tsukasa the belt and book, allowing him to transform into Kamen Rider Decade by using a card from the book and inserting it into the belt.

Arriving in the World of Kuuga, Tsukasa takes the guise of a policeman and watches Kuuga destroy a pair of Grongi, Ra-Dorudo-Gu and Me-Gyarido-Gi, before reverting to his human form, Yusuke Onodera. Tsukasa later destroys Go-Baberu-Da as Decade, but is mistaken for a Grongi by Yusuke and Ai. When Yusuke and Ai arrive at the Hikari Studio to discuss this strange Grongi, Tsukasa offers Ai his help in solving the mystery behind the Grongi's female targets and the location of their lair. On the foot of Mount Hitoki, the Grongi's Lair, Tsukasa reveals he used Ai as bait to lure out the remaining Grongi, revealing their plan to revive their leader before ruining their game. While attempting to destroy the Grongi, Decade is attacked by Kuuga, who reveals he knows about Decade's mission and will stop him at all costs.

After fending off the Hoppers who disappeared into another dimensional rift, Yusuke reveals he was told of Decade by a mysterious man. When Ai and her task force go to investigate Mount Hitoki, a black mist begins to rise from within, signaling the revival of N-Gamio-Zeda. Resurrected by the dimensional chaos, he uses his miasma to convert humans into Grongi. While Yusuke saves Ai and takes her to the hospital, Tsukasa fights the Grongi alone. A dying Ai requests Yusuke to overcome his angst and fight to protect everyone's smiles, and so Kuuga and Decade work together to destroy the remaining Grongi. N-Gamio-Zeda, in a last effort, absorbs all the Grongi to power himself up, but he is ultimately overpowered by both Decade and Kuuga, who destroy him with a combo attack.

Arriving in the World of Kiva, Tsukasa and company discover that the Fangires of this world have made a truce with the humans. However, when Tsukasa finds the Lion Fangire attacking a young woman, he transforms into Decade to fight him. Wataru, the King of the Fangire Race, witnesses this and becomes Kamen Rider Kiva to fight him with the aid of his Arms Monsters, forcing Decade to assume Kamen Rider Kuuga's Mighty, Titan, and Dragon Forms to counter. Yusuke manages to stop the fight, and the Swallowtail Fangire reveals that the young woman was actually a renegade Fangire. Yusuke reveals he has promised to help Wataru because he is uncomfortable with being the King.

As Tsukasa is fighting against Kaixa in another dimension, the Beetle Fangire defeats Wataru and becomes the new Fangire king, claiming Kivat. After the new King dissolves the truce, Yusuke arrives to protect Wataru before the boy runs off. After Yusuke expresses his reasons for helping the dethroned boy, Wataru takes refuge in the Hikari Studio. After being caught up on current events, Tsukasa makes his way to Castle Doran to save Yusuke as the Beetle Fangire absorbs the Arms Monsters into himself. After destroying the Swallowtail Fangire, Decade encounters the Beetle Fangire, who assumes Kiva's DoGaBaKi Form. When their fight makes its way to Yusuke and Wataru, the boy finds his courage to overcome his Fangire impulses and declares himself the King once more.

Upon arriving in the World of Ryuki, Natsumi goes to the Atashi Journal headquarters to learn about the world's Kamen Riders from its editor, Reiko Momoi. After Natsumi's arrival at the journal's offices, Reiko is mysteriously murdered, leaving Natsumi as the culprit as she had a small fork in her hand. Natsumi is arrested under suspicion of murder, and is to be sentenced with a Kamen Rider Trial: a system where Kamen Riders fight in the Mirror World to determine the outcome of criminal cases. Natsumi calls upon Tsukasa to be her lawyer, who meets with Shinji Tatsumi to hear what he knows of what happened to Reiko. As Shinji reveals that he is Kamen Rider Ryuki and he believes Natsumi was framed, his former friend Kamen Rider Knight is fighting in the Kamen Rider Trial, defeating several opponents. Shinji suggests to Tsukasa that he should fight as Decade in the Kamen Rider Trial to clear Natsumi's name.

After defeating Knight, Decade is about to finish him off when Ryuki pleads with him not to deliver the final blow, as he feels Knight must answer for his crime by his hand. However, Abyss uses this time to make his move to take out all three Riders at once, forcing them to retreat with Ren refusing to answer Shinji as he leaves. After her brief encounter with Narutaki, Natsumi learns that Shinji and Tsukasa are convinced that Ren is Reiko's murderer, although Yusuke sees otherwise. Meanwhile, a wounded Ren battles Kamen Rider Odin and defeats him, emerging from Mirror World with Odin's Time Vent as Shinji and Yusuke find him. Learning that Ren obtained the card to save Reiko, Shinji uses the card to go back in time as Tsukasa holds Abyss off. Arriving seconds before Reiko's death, Shinji and Tsukasa manage to save Reiko with the latter cornering her true murderer, Kamata.

Upon arriving in the World of Faiz and once more encountering the mysterious Daiki Kaito, Tsukasa finds himself in a school uniform and enrolled at Smart Brain High School. He learns that the high school is attacked on a nightly basis by beings called the Orphnoch, with only Faiz to protect the school. Daiki challenges Tsukasa to find out who Faiz is, and Tsukasa then challenges the Lucky Clover clique to a tennis match to see if any of them are Faiz. He beats them, learning that they are Orphnoch who are also after Faiz, and is forced to become Decade, using Blade's power against them. However, Decade is outclassed when Momose appears as the Tiger Orphnoch and warns him to back off.

After Tsukasa recovers the Faiz Gear, he learns Diend's reasons for wanting the belt before Takumi regains it so he and a shocked Yuri can escape on the Autovajin. However, as he exposed himself as the Wolf Orphnoch to protect her only to be forsaken, a saddened Takumi attempts to dispose of the Faiz Gear into the river. Managing to save the Gear while following him, Tsukasa returns to the photo studio where he put Yuri's confusion at ease. The next day, Daiki attacks Takumi to get the belt from him, nearly killing him when Tsukasa arrives with it. Refusing to take Tsukasa's words of something more precious than the Faiz Gear seriously, Daiki takes Decade's Ride Booker, and Narutaki takes advantage of the situation as he takes Tsukasa into another dimension to be killed by Kamen Rider Ryuga.

Upon arriving in the World of Agito, Yusuke is shocked that there are Grongi in the world which are being dealt with by Kamen Rider G3-X. He is further shocked when he sees an interview with Toko Yashiro, who is physically identical to the Ai Yashiro that died back in the World of Kuuga. Arriving at the police station, Yusuke offers to be the new user of the G3-X suit, but loses the position to Kaito. While this occurs, finding himself in a mailman outfit with a letter to Shouichi Ashikawa, Tsukasa and Natsumi find the man before they are attacked by what they think to be a Grongi. But during the fight, Tsukasa realizes he is fighting an Unknown, an Ant Lord called Formica Pedes.

After Yusuke saves Tsukasa from Delta's attack, Gills is about to fight when he's overcome with pain as the Unknown shows up to kill him. As Shouichi escapes, Toko recognizes him via G3-X's camera. While Tsukasa insists on protecting an annoyed Shouichi, Yusuke reports the defeat of the Grongi and the emergence of the Unknown. He finds Toko saddened, but has little time to help her as Kaito takes the G4 chip stored within his locker. Yusuke demands the chip back, but during the struggle, Toko blasts the chip to bits and a disappointed Kaito leaves. The next day, as Tsukasa continues to keep Shouichi safe from the Unknowns' attack, Yusuke learns that Shoichi was the original user of the G3 suit when he receives the letter for Shouichi from Toko.

After Gremlin's defeat, Haruto is lost in the World of Kaijin, a parallel world where it is inhabited by monsters created by an entity called Amadum who wants to steal the powers of the Kamen Riders for himself. Using the Legend Rider Rings, he will summon 13 Heisei Kamen Riders.

Haruto and Kosuke must defeat Amadum before he can use the Rider Rings to transform their world into a kaijin's paradise.