It's set in a magical version of ancient China and it's terrifying... but only as a portrayal of a historical society more alien than I'd be able to handle. Living there would be hell. (The anime also has ghosts, vampires, demons, etc. but they're run-of-the-mill fictional undead and nothing unremarkable.)
Our cast lives in the imperial palace, where no one's gonads are their own. No, not even the emperor's. He gets in trouble if he doesn't visit his consorts often enough.
1. If you're male, you're a eunuch. (Visiting the inner palace is prohibited for uncastrated and non-royal males. Even children have been snipped.)
2. If you're female, your highest available ambition is to become a consort, i.e. providing sexual services to the emperor. (There's also a red-light district for everyone else's prostitutes.)
That's not the scary bit, though. That would be the people and the cheapness of life. Execution is the routine punishment for almost anything. Adultery? A child killing a bird? All punishable by decapitation. An entire bloodline can get sentenced to death, even including the children. Suicide is commonplace, e.g. hanging yourself or stabbing yourself in the throat. The court's a nest of vipers. A woman who had her tongue cut out to silence her is pretending to be illiterate, because she'll be killed if it's learned that she can write. When they were children, both of the show's protagonists saw their mothers murdered. One later found her mother's severed head and got enslaved, while the other's best friend was tortured to death for no reason except that he'd been the emperor's friend. It's hideous. There's incest, with love between half-siblings. (Two of them pass on to the next life together.)
"Well, of course. That's how everything works around here. Even when the emperor's birth mother was killed, a lady-in-waiting was framed for the crime and executed for the sake of appearances."
The protagonists are safe-ish, though. Safer than anyone else, at least. Ka Koushun is the emperor, so he's only in danger from his relatives. Ryuu Jusetsu is the Raven Consort, a mysterious figure who never performs a consort's bedroom duties but instead lives in a palace and is supposed to never associate with anyone.
To Jusetsu's annoyance, Koushun keeps visiting her. She doesn't want a friend and keeps telling him to sod off, but he bribes her with food and gets her help on magical mysteries, usually involving ghosts. The dead are everywhere in this show. Jusetsu's powers mostly work on them.
Despite itself, the show's actually quite nice. There are good people in this screaming bloody nightmare of a world, if you look for them. Jusetsu puts up a rude front, but she's lonely underneath and doesn't know how to get on with people. On being invited to become Koushun's friend, she has to ask what friends normally do. She does a lot of good over the course of the series, albeit often reluctantly.
The only glitch is the voices. The eunuchs don't have high-pitched voices, even though we're told that it was normal for them to get snipped in early childhood.
This is a classy show. I'd even say "elegant". You could call it a slow-burning impossible romance between its two lead characters, since I'm pretty sure court rules wouldn't let them get together. It tells ghost stories, some haunting and some disturbing. The only thing I didn't like here was the official subtitles using Chinese readings for everyone's names, which isn't an indefensible decision for a Chinese-ish-set story but is distracting for anyone who's listening to the Japanese voice actors and their Japanese readings. (Ka Koushun becomes Xia Gaojun, Ryuu Jusetsu becomes Liu Shouxue, etc.) Your eyes and your ears are at war with each other... and you can't just turn off the subtitles unless your Japanese is so good that you can follow antiquated period language.
Would I watch a second season? Yes, definitely. Will I keep the episodes? Probably not, but it's got me interested enough to consider looking for other Japanese anime with a similar "approximately ancient China" setting. The Story of Saiunkoku, for instance. I might report back...