For some context, I've watched 'Kamen Rider W' ('W' is pronounced 'Double' in this context by the way) and 'Begins Night' before the anime but did not read the post-story manga (which is what the anime is based on). Continuing off of Fuuto Tantei/Fuuto Pi, Shotaro explains how it all started: the origins of him, his job, how he received the Double Driver, and how he first met Philip. This movie is essentially a retelling of the 'W' portion in the movie: "Kamen Rider × Kamen Rider W & Decade: Movie War 2010" Due to my prior knowledge of the 'Begins Night' event, I felt a littleimpatient getting to the "new stuff". The majority of the movie is a flashback, but there are some minor differences from the live-action version most of which are just extra scenes and details but one scene somewhat conflicts with another of W's live-action movies but is ultimately not important for the viewer to know or anyone to really gripe about.

The ending of this movie is where the anime continues off hinting at further plot developments should Fuuto Pi get a second season and I really do hope we get more seasons.

The art, animation, music, voice acting, and sound design are all great. Absolutely no complaints there. I wanna say that the pacing is a little slow but I think that's just me being impatient due to me already knowing the main gist of the flashback. Ultimately, I recommend watching it if you're a general fan of Kamen Rider or have already watched Fuuto Tantei/Fuuto Pi.