WARNING:This movie contains scenes of physical fights and gambling. Viewer discretion is advised!
Kamen Rider Gaim Gaiden: Kamen Rider Knuckle (仮面ライダー鎧武 (ガイム) 外伝: 仮面ライダーナックル,Kamen Raidā Gaimu Gaiden: Kamen Raidā Nakkuru) is the second installment of the Kamen Rider Gaim Gaiden 2 sequel series of V-cinema films, which this particular installment is set after the series' finale. It focuses on the character Zack as he returns to Japan to stop an exiled Team Baron member from dishonoring Kaito's legacy.
This installment reveals the past of Team Baron prior to the series.
It's been one year since Kaito disappeared, and peace had returned to Zawame City once more. Zack departed for New York, and left leadership of Team Baron to Peko. However upon hearing that Shura, a former member of Team Baron that Kaito once exiled, had formed his own team, Neo Baron, Zack returns to Zawame City to set things right.
After a year of the Helheim incident had ended, the Beat Riders group alongside Zack had talked on their current living peace. Hideyasu won an award for his pastry and become the second in charge in Charmant II and Mitsuzane worked hard to help Takatora. Zack, thinking on his dream, decided to advance his dance career in USA. Meanwhile, a mysterious person had just finished on his self training boxing screamed on Kaito's photo and announced that he would inherit his will to make the weak one to be destroyed and the strong should live.
Many days had passed, Zack had failed himself on his carreer in the USA. One of his friend in the USA talked to Zack about Neo-Baron. Zack was surprised and got a call from his former pre-Baron teammate, Azami that Peko had disappeared after he had learned about the Neo-Baron.
Zack returned to Japan and gathered the information about Neo-Baron as much as he could. He was then informed by Hideyasu about the Neo-Baron to be an underworld gang group which created their own underground fight with a violent rule. Zack was shocked to learn who was behind the group's birth, Shura and advanced to the Neo-Baron's base to settle things with him after Hideyasu told the location of the base.
After Zack had arrived, Zack got another shock again that Peko was in there and gathered the money gamble for making the pool winner of the fighters. As Zack insisted for Peko to get out with him, Shura provided Zack a challenge to face his best fighter. When Zack won against one fighter, Shura called for more instead and showed Zack a Sengoku Driver, transforming into the black version of Kamen Rider Baron and advanced to defeat Zack. Zack managed to get away alongside Peko after Oren came to intervere.
As they managed to get out, Zack yelled at Peko for what he had done. Peko cried and begged for forgiveness as his true intention was to stop Shura, but Shura's strength had subdued him and he had no choice but to follow him to keep alive. Zack understood of Peko's sadness, telling him about his failure life in the USA, especially because his leg was yet to be in full recovery.
It wasn't long as a group of Kurokages appeared, but Mitsuzane arrived as Kamen Rider Ryugen Budou Arms to finish the group off. Mitsuzane explained that the data of the Sengoku Driver that Yggdrassil had made was leaked and being sent to many evil organization. Unfortunately for Mitsuzane, he only had time to take one new rebuilt Sengoku Driver and presented it to Zack with his Kurumi Lockseed alongside Marron Energy Lockseed. Mitsuzane explained that Marron Energy would be useful with the Neo Genesis Driver, but Zack informed that Kaito's Neo Genesis Driver's had been destroyed. Soon, Shura called Zack for coming to him as he had taken Azami as his hostage.
Zack asked Peko to go to Baron's base and took the core on Neo Genesis Driver while he was going to save Azami. After Zack had arrived, Shura let go of Azami as he promised and called on his minions to face Zack. Zack transformed into Kamen Rider Knuckle Kurumi Arms and made the quick work with the Kurokages, but he couldn't defeat Shura the Black Baron as Knuckle's lockseed's power is far inferior than Black Baron. Right after he was knocked out from his transformation, Peko arrived and gave Zack the core from Neo Genesis Driver. Going for the second round, Zack transformed into Kamen Rider Knuckle Kurumi Arms Jimber Marron. With increasing power from Marron Energy Lockseed, Zack able to fight Shura properly and after their fierce fight, Zack won the fight.
Unfortunately for Zack, the timing when he got the Genesis Driver's core was a late enough to make him become very tired because of his injuries. As the result, Zack was fallen with Peko and Azami screamed on him, begging him to wake up. For an unknown explanation, Zack stood on the Baron's dancing stage with Baron's uniform on as he spoke to himself for unable to understand Kaito yet. Kaito's spirit appeared and told Zack that it was impossible for Zack to understand him. Zack requested for a dance with Kaito afterward.
It is unknown how Mitsuzane was able to carry the briefcase containing Zack's new Sengoku Driver and Lockseeds within his person when he was seen transformed into Ryugen beforehand.
The flashback here used to describe Kaito's defeat was the one taken from the alternate future instead of the actual battle where Lord Baron was fighting Gaim Kiwami Arms.
How Zack survived from his fight with Kaito in episodes 45 to 46 is revealed at the start of Knuckle portion.
Similar to the Kamen Rider Gaim Gaiden: Kamen Rider Baron, this movie also retcons the past story as stated in REAL RIDERS: Kaito Kumon Side Story: Kaito creates his own team before recruiting Zack and Peko. But in this movie, he instead take over Zack's team and Peko already joined this team before being reformed as Baron. However, the same story line when Zack joined Kaito after his defeat is still intact despite the condition is reversed as Zack didn't ask Kaito to join in the light novel.