In short: a standard everyday Japanese boy named Yuri is going through a normal day, when he accidentally gets flushed down a toilet into another world. Yes. A toilet. Honestly, considering how many isekai stories there are now, this was a refreshing parody ahead of its time.
Yuri arrives in a fantasy land of swords, magic, horses, and strife. And immediately finds out...he's the demon lord!! Except wait. Despite that frightening title, demon lord doesn't really mean much. Demons in this world are basically just a race of humans, except with more magical talent and longer life spans, that have their own Kingdom and culture...but are otherwise still humans. (Honestly they looked exactly the same as humans and acted exactly the same, and I wasn't sure why the story decided to call them demons, but eh.)
Suddenly appointed to Kinghood, Yuri struggles to know just how he fits into this magical new world and how he'll handle an ongoing war. But good news, he's got lots of retainers to help him out, and whole vassals of royal families, and also his fiancé. Though, much to his chagrin, said fiancé is male, since Yuri attempted to insult the boy by slapping him across the face, and didn't realize that in this world, that was a proposal of courtship. Whoops!
The whole show is on that level of silliness. It's a comedic adventure romp, that happens to also have a solid fantasy story going on at the same time. Despite the layers of slapstick comedy, the show does manage to have a fairly competent adventure plot -- with some political intrigue, dramatic backstories, and quests throughout the country for Yuri to journey upon. The quality of storytelling does fluctuate. Some of the filler episodes notoriously transform the characters into idiots running right into danger and spouting out-of-character platitudes for twenty minutes straight. But when the main story is happening, the writing shapes up and manages to be surprisingly good. I was into the series mostly for the comedy, but ended up staying for an unexpectedly decent fantasy adventure.
The anime was released during a time where shows were expected to have longer runs, so Kyo Kara Maoh has over 80 episodes to build up its world and characters, which is a good thing. Too many fantasy genres in anime get squished into the 12 episode limit of one-season, and thus aren't capable of building their story correctly. So it's nice to see a fantasy story that had time to shine (and also be a completely silly mess.)
There's also an ever-present BL vibe through the whole thing (as might be obvious by our main character getting formally engaged to another boy by the second episode) so many of the side characters have flamboyant tendencies. For me, this was a welcome addition in most cases as I found it hilarious, and it again parodied the usual "boy falls in fantasy world and suddenly gets a ton of hot elf girls" by instead giving the main character...more and more middle aged dudes to deal with. (Though the joke with the purple-haired guy clinging to Yuri did get old eventually.)
So don't watch this with the family unless they're all okay with some very openly BL humor, often held in bath scenes.
It's a feel-good show and silly adventure that occasionally dips into a darker, more serious fantasy plotline. It's not perfect. There's definitely some budget animation, dumb moments, and pretty bad filler episodes. It has some preachy speeches, and Yuri can come across as a naive pacifist (though it is eventually explained why he's like that, more than just being inexperienced.) But it's nice to watch Yuri's desire to stop war through peaceful means, and see how it changes his commanders' ways of handling the situation. It's something you want to believe in, even if it does come across as childish.
I just can't help but like this stupid show.
