I originally posted this as a discussion post, but realized this may be more helpful as a guide!
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I was really struggling with getting Victim: Yasuhiro Hagakure (Demo) to appear in the movie gallery. Like many others I was so frustrated because it was the last thing I needed to get the Rogue's Gallery achievement and 100% the game.

I looked at other forums suggesting playing the prologue in Chinese (can be done through Steam properties) and I did as such and got nowhere. Other forums mentioned playing the us_only beta, but it didn't show up for me so I think they removed the beta from Steam a few years ago. But, I finally did something that made it appear for me so maybe it will help someone else!

Firstly, I think this must be a mac issue. I had played the entire game on my macbook and encountered this problem. The way I solved the problem was I downloaded the game onto a windows PC. Make sure your game data is saving to the steam cloud so you can load the same game data. Then I went to chapter select and rewatched the epilogue. I didn't skip the credits, so I have no idea if it has any bearing on it, and in the moment I didn't want to risk it. Only then did the video show up in the movie gallery!

I'm really hoping this can help other people experiencing this issue because I know I was losing my mind trying to figure it out.