Directed by Naoyuki Itō and animated by Madhouse, Overlord: The Sacred Kingdom is a continuation of season four of Overlord, the anime.
The actual plot of the film has almost nothing to do with the series. You can watch it thinking it's a high fantasy film about invasion and war, and only be confused a couple of times.
The plot: the Sacred Kingdom has been attacked by the Demon Emperor Jaldabaoth and his army of half humans (half pig, half wolf, and so forth). The kingdom's best paladin, Remedios Custodio, leads a small team to the neighbouring Sorcerer Kingdom to ask for aid.
His Sorcerous Majesty is a huge skeleton, an undead, and the focus of the film. He is not the main character, however. That would be Neia Baraja, a squire, who is assigned as an attendant to the skeletal Ainz Ooal Gown.
What's not explained in the film is that this is a video game. A MMOPG, to be precise, that the player behind Ainz Ooal Gown got stuck inside of when the game was officially shut down. He searches for other humans, and the conquers the virtual world.
In Overlord: The Sacred Kingdom, we see a lot of manipulation, a PR campaign really, that would have been better spaced out throughout the plot rather than revealed in the last five minutes. There are interesting themes of justice and sacrifice, particularly in regards to hostages, a trolley problem sort of situation.
The animation is very well done. Ainz Ooal Gown rides a skeletal horse that's in flames, so that's cool, too. There's many females characters, but they don't feel very well roughed out.
Then again, no one does. Not even the battles, which mainly consist of cries of "fire ball"... Then again, I haven't read the manga or watched the anime, so there's a lot that the unsuspecting viewer will see missing, while it's already happened.
The film is now playing throughout North America, only in theaters. Visit the official site for locations and showtimes.