Kamen Rider Decade: All Riders Super Spin-off

Sayo identifies Tsukasa Kadoya as her older brother when he arrives at the manor in the AR World. This revelation suggests Tsukasa's true origins lie in this world, though he has lost his memories of his past life there. The connection is later reinforced when Sayo reveals details about Tsukasa's childhood at the Kadoya mansion.

Earlier, Tsukasa's photos from this world come through with striking clarity, hinting at a personal connection to the realm.

Tsukikage reveals that the Rider Battle, a contest to determine the strongest Kamen Rider, was designed as a potential remedy to the crisis caused by the Nine Worlds fusion. However, it is later revealed to be a ruse engineered by Dai-Shocker to secure dominion across the saved worlds. The battles were a cover for their larger scheme.

Tsukikage presents the Rider Battle as a solution immediately after the Nine Worlds fusion begins influencing the World of Decade.

Natsumi refuses to forgive Tsukasa after he attempts to reconcile at the Hikari Studio. She cannot bring herself to forgive him for using her as a means to achieve his goals throughout their journey. This rejection leaves Tsukasa without his closest ally and forces him to face the final battle with few friends remaining.

Earlier, Tsukasa sends Natsumi and Yusuke into the sewers to shield them, showing his pattern of making unilateral decisions for others.

Sayo uses the Earth Stone on Yusuke, which unlocks Kuuga's most dangerous power within him, transforming him into Kuuga Rising Ultimate Form. However, this power is controlled by Sayo (as Bishium), forcing Yusuke to battle against his will while trapped in the sewers. He pleads with Natsumi to run as the unleashed force surges through him.

Sayo and Tsukikage have aligned with Dai-Shocker, making her decision to use the Earth Stone a deliberate act of betrayal.

Doctor Shinigami reveals that all the prior Rider Battle matches were engineered to secure Dai-Shocker's dominion across the saved worlds. The nine worlds fusion, triggered by Tsukasa's journey, presented an opportunity for Dai-Shocker to expand their control across multiple realities by using the Rider Battle as a cover for their conquest.

After Decade's victory in the stadium, a castle rises from the ground, signaling the start of Dai-Shocker's overt invasion.

Sayo aligns with Dai-Shocker as High Priestess Bishium, revealing she and Tsukikage have been working with the enemy all along. This betrayal comes to light when she uses the Earth Stone to control Yusuke's Kuuga power. Later, she awakens to the consequences of her choices, destroys the Earth Stone, and frees Yusuke from its hold.

Tsukikage admits he has outlived his purpose and sinks into the sewer, suggesting their alliance with Dai-Shocker was always temporary.

After King Dark awakens from the wreckage of Dai-Shocker's castle, Diend arrives with Kamen Rider J and uses the DecaDriver Final FormRide card to transform Decade into Jumbo DecaDriver. J becomes Decade Complete Form Jumbo Formation, then delivers a Dimension Kick that destroys King Dark, using the other Riders as enormous Kamen Ride Cards for the finishing blow.

Diend has been gathering strength throughout the battle, waiting for this moment to deploy the powerful Final FormRide.

Kamen Rider W makes a striking entrance during the climactic confrontation at Dai-Shocker's castle. He takes down Shadow Moon and then slips away, leaving the war to the other Riders. His unexpected arrival tips the balance and helps turn the tide against the enemy forces, allowing the Riders to perform the All Rider Kick.

The battle reaches its peak with multiple Riders converging, creating the opportunity for W's dramatic intervention.

Tsukikage confronts Tsukasa about leaving his sister alone for so long, creating tension when they reunite at the manor. Tsukasa had lost his memories, which explains why he was absent from Sayo's life. This backstory adds emotional weight to Tsukasa's journey of rediscovering his identity and reconnecting with family.

Tsukasa's memory loss prevents him from initially recognizing Sayo or understanding his connection to the AR World.

King Dark awakens in the wreckage after the All Rider Kick destroys Dai-Shocker's castle and defeats Shadow Moon. Diend arrives with Kamen Rider J, and using the DecaDriver Final FormRide, they transform into their jumbo forms to deliver the final Dimension Kick that destroys King Dark, using the other Riders as giant Kamen Ride Cards.

The blast of power from the All Rider Kick awakens King Dark, suggesting a final threat remains after the castle falls.

Joji Yuuki confronts Tsukasa seeking revenge for the arm he lost while working for Dai-Shocker. When he realizes Tsukasa has changed and now stands in the crosshairs of Dai-Shocker's plans, Yuuki rips away his own arm to reveal a robotic replacement, enabling his transformation into Riderman to join the fight against the organization.

Yuuki's arm loss while serving Dai-Shocker sets up his personal vendetta against both the organization and Tsukasa.

Eijiro reappears at the end as if nothing happened, which the narrative presents as a paradox resolved. This signals that the timeline has been restored following the defeat of Dai-Shocker and King Dark. His return hints at future adventures in the worlds the Riders saved, suggesting the multiverse has been stabilized.

The narrative emphasizes memory, courage, and bonds forged across worlds as key themes that can shape the future.