This installment reveals the past of Team Baron prior to the series.
to be added
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.
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.