In the scene, Gamio suddenly transformed into countless streams of black smoke, rapidly floating out of the mountain. At the same time, in a hospital, a news report aired on TV:
"The black smoke coming out of Dengrong Mountain has been confirmed to contain harmful gases. A large number of unknown life forms have also been detected in the black gas."
Kadoya Shi arrived at the hospital and asked Yusuke, "How is Yashiro?"
Onodera Yusuke replied worriedly, "She's seriously injured. She inhaled a lot of the black gas. If this continues, she'll solidify!"
Kadoya Shi's expression darkened. "The Gurongi race is inherently aggressive. If all humans become Gurongi, the world will end."
Yusuke's face also grew anxious. "Didn't Kikiru fail? Why is this happening?"
Kadoya Shi explained, "That being wasn't supposed to awaken. But, just like when our world was attacked, a phenomenon of destruction has appeared."
Yusuke looked puzzled. "Our world? What does that mean?"
Kadoya Shi answered calmly, "We come from other worlds."
"To save this world!" Natsumi Tachibana added.
"Save the world?" Yusuke was shocked. He hadn't expected these two to be from other worlds. Could such worlds exist? It was incredible!
Meanwhile, the black smoke continued to spread, drifting toward the city. The sky turned ominously dark, and people on the streets began screaming in panic. Monsters emerged from the smoke, massacring ordinary citizens. Chaos engulfed the streets as crowds fled in terror.
Kadoya Shi, seeing more people turning into Gurongi, resolved to stop the monsters. However, Natsumi Tachibana ran over with a worried expression. "Shi, you'll become a Gurongi too! The gas in the smoke is poisonous and terrifying."
Kadoya Shi responded, "I'm not from this world. Perhaps I'm the same kind as the Gurongi! If we're the same, what's there to fear?"
The streets were now filled with monsters, some even sprouting wings and flying into the sky. The audience across the three realms watched, their brows furrowed in horror. It was like the end of the world—humanity was nearing extinction, leaving only demons to dance amidst the chaos.
On a tall building, Gamio stood arrogantly. "Humanity will merge with Gurongi! Darkness will consume everything!"
At that moment, Kadoya Shi confronted Gamio. The latter remarked, "You are neither Kuuga nor human. It seems neither you nor I belong to this world."
"What do you know?" Kadoya Shi asked coldly.
Gamio replied, "Humans will inevitably become Gurongi and destroy each other. This is fate."
Kadoya Shi retorted, "I share your view that humans fight and destroy. But I also know someone who fights so others can smile. Even if he falls into darkness, he wants to protect humanity. I believe in him."
The audience of the three realms was deeply moved. Kuuga fought to protect humanity's smiles, making him a true hero. Kadoya Shi's determination to protect Kuuga's smile added another layer of emotion.
"Who are you?" Gamio demanded.
Kadoya Shi took out his belt. "I'm just a Kamen Rider passing by. Remember this! Transform! Masked Rider Decade!"
The fight began. Kadoya Shi attacked Gamio but was knocked down with a single punch. Monsters swarmed him, and though he fought back valiantly, it was difficult. Just as Kadoya Shi seemed trapped, Yusuke arrived on a motorcycle, scattering the monsters.
"You're here!" Kadoya Shi said.
"I'm here to fight too—to protect humanity's smiles!" Yusuke replied firmly.
Gamio unleashed a massive pillar of fire, akin to a nuclear explosion. Flames filled the screen, leaving the audience in awe of the cinematic spectacle. Despite the chaos, Kadoya Shi and Yusuke continued to fight back-to-back, using their belts and powers to fend off the monsters.
Kadoya Shi activated a new form for Yusuke, transforming him into Kuuga Golem. The two launched a combined assault on Gamio, who absorbed other monsters to increase his power. Lightning and fire erupted from Gamio as he retaliated with overwhelming force. Yet, Kadoya Shi and Kuuga Golem countered with equally powerful attacks, eventually forcing Gamio into retreat.
The climactic battle ended with Gamio's body engulfed in flames and his final words, "Humans, the darkness will dissipate," before he exploded into smoke. The mysterious man observing from afar vowed, "I will never forgive you, Decade!" and disappeared through a dimensional wall.
As the dust settled, Kadoya Shi and Natsumi Tachibana reflected on their mission. "Our work in this world is done," Kadoya Shi said. However, he added, "I need to recover my lost memories."
The audience was intrigued. What memories had Kadoya Shi lost? They eagerly anticipated the day he would regain them.
Meanwhile, another subplot unfolded. Yusuke was taken to a mysterious world by a white bat. The scene shifted to a comical encounter with a monster from the Yagui tribe, who claimed to be discriminated against by humans. The monster's exaggerated antics provided a humorous reprieve amidst the tension. The audience was left amused and curious about this new development.
As the story closed, Kadoya Shi and his allies prepared for their next adventure, leaving audiences eager for more.