[vin13ish]

The plot Synposis contain some of stuff that didn't get explored in the show

"A continuation from the TV series, this is the story of Makoto, Alain, and Kanon who have traveled back to the Ganma World. An encounter between Makoto, Alain, and their friends will take place. It will explain the connection between Makoto and the other Makoto. Kanon’s secret will be revealed as well.

A new story is born from Ghost! Kamen Rider Specter/Makoto Fukami’s secrets are revealed!"

I assumed Kanon's Secret will be the one where she was Eyecon at beginning of the show. I feel this movie will finally reveal of how did Kanon become Eyecon at first place. It will probably be a flashback sequence