When I started Sengoku Rance for the first time instead of the intro playing after the logos the sceen went black and I heard only the music playing. After closing the program and running it a second time the start menu displays without problems. However, if I remove the flag file from the save folder to try to replay the intro the same problem persists. My machine has WIndows 11 installed, so I tried to run the game in compatibility mode for Windows 8,7 and XP but it did not solve the problem.
I looked at the video file in the game folder and the intro movie is classified as an ALM file. I have never heard before of this format, so I do not know what I am supposed to do to make it work.

Does anyone know how to make the intro video play properly?

Hey bud I know this is years after the fact but I just bought the game to support the devs and the intro video played fine for me on windows 11. Did you ever get your working?

Actually...yes! I really do not know why, though. After completing two routes, I made a pause and recovered the game after a few months. I tried removing my save files and see if the intro played and that time it worked flawlessly. I did not do anything special, so I really cannot understand what was wrong with my pc. I remember reading somewhere that Windows 11 got at some point an update regarding the video codecs, so it could be that update fixed the problem.
Anyway, this was only a minor nitpick. The intro plays only the first time you run the game, after that the only cutscene is the final credits that can easily be skipped.

To conclude, big thanks to MangaGamer! I contacted them asking for help and to my surprise they answered and offered extensive help, proposing various solutions. In the end no one worked, but still that they tried their best providing technical support for a 17 years old game is very laudable.