One of the many entries in the Garo universe, a tokusatsu franchise that has been going strong for the past 15 years. I'm not too familiar with the particulars, I never watched the original series, even so these stories tend to be so generic that it's easy enough to cherry-pick some spin-offs without missing anything essential.
This spin-off deals with the backstory of Barago and Kiba, an old spirit who inhibits a Makai Armor. It ties in with the plot of the original series and it features some of its cast, but ultimately it's a pretty simple story of good vs evil, featuring a more than adequate amount of demonic battles. If you get lost, you simply need to watch more fantasy anime.
What stands out the most is the art style here. I'll readily admit that not everything works and some parts look really cheap, even so the mix of different animation styles and live action is intriguing and gives this film a unique vibe. There's quite a lot happening in the short runtime and if you're looking for a fun but cheesy diversion, this short spin-off has you covered. Just don't expect anything grand.