This summary pretty much spells out the main plotline for the entire movie, you have been warned.

Gavan appears before the Gokaigers and Gavan overwhelms the Gokaigers and arrests them, handing them over to the Galactic Space Police. Meanwhile, Gavan realises there is a conspiracy going on and is attacked by Gavan Bootleg, which the Space Police and the Zangyack built together and Gavan is sent into Makuu Space. The Gokaigers get ready to the enter Makuu Space, but returning may not be possible once entered. Can they safely make it back?!

Lastly, the article from OCN, asks the question :

By the way…who is this?

Notice how he’s wearing Doggie Krugers belt? In an earlier stage show, they did state Doggie and Gavan were friends. Possibly a larger plot point or just a reference? He hasn’t been confirmed as a character, so at this stage, it’s more likely the latter.