It's a shounen anime about onmyouji (exorcists) who fight basara (demons). Rokuro is a brash fourteen-year-old boy who used to be the strongest young onmyouji until something bad happened and now he doesn't want anything to do with it. He refuses to fight. Meanwhile Benio is a serious-minded fourteen-year-old girl who's dedicated herself to basara-extermination and thinks Rokuro is a loud, useless failure. (She's not entirely wrong.)
You can imagine the surprise when Arima Tsuchimikado (the leader of all onmyouji) announces that Rokuro and Benio will marry and have a baby. Rokuro calls Arima "perverted pants man" for the rest of the series, for a start.
I enjoyed a lot of this show, but it goes downhill a bit. I'd divide it into three phases.
EPISODES 1-20: based on the manga, albeit apparently with lots of filler and original stuff that was nonetheless invented by the manga author. All this is pretty good and at this stage I thought the show was excellent. We learn about the backstory of our heroes. Shocking things can happen. Rokuro and Benio don't get on at all at this point, so the character dynamics are all up in the air. This is also complicated by Rokuro having a childhood friend, Mayura, who likes him. (Gentle, buxom, yellow-and-green hair, enormously likeable).
EPISODES 21-37ish: anime-original, with a two-year time skip just to increase the sense of a reboot. (Benio, Rokuro and Mayura are now 16.) The show also moves here into a ten-week cycle, each time marked by story arc climaxes and a new title sequence. I enjoyed this phase too, but it does introduce the annoying basara Suzu and her song-and-dance numbers (OW OW OW OW, STOP IT, KILL ME NOW THEY'RE DANCING). Nonetheless the Sae story arc was intriguing, the Rokuro-Benio relationship is still unfolding and the show's still capable of surprising darkness.
EPISODES 38ish-50: anime-original and... oh dear. I got a bit bored and they started squashing my good memories of the earlier episodes. The show goes into Big Bad phase, so Rokuro has to fight a baddie! Then another baddie! Followed by yet another baddie! It's too much fighting, with the show seemingly incapable of doing anything dramatically interesting in this mode. There's one huge exception to that, with Benio, but even that's a disappointment when the show fails to follow up on what had been a shocking decision. It also doesn't help that the Rokuro-Benio relationship is now almost resolved (bar one unspoken thing that's nagging at Benio), so we start getting story contrivances to stop things from settling down there.
The very end's quite good again, though. Once it's no longer encumbered by battles and baddies, it's as if the show's relaxed back into just doing what it does well.
Overall, I think it's a good show that lets itself down once it gets into Shounen Battle Mode. There's some intelligent writing in here, if you can persuade yourself to look for such things in demon-fighting shounen stuff. Unfortunately I didn't like all the cast. I never warmed to Shimon, or indeed Seigen. The Twelve Heavenly Commanders tend to be one-note characteroids rather than people, with by far the worst being the money-grubbing Kengo Uiji. He just can't shut up about it. Suzu will make your brain explode with her rap, but personally I couldn't take her split-personality speech patterns either. (She's much better in her final appearance, though.) The least bad of my grumble characters is perhaps Benio's pointless familiar, Kinako, whom I didn't really mind but equally I wouldn't have noticed if he'd fallen under a bus.
That said, though, I liked the core cast and everyone at the Seika Dormitory, who ground Rokuro and connect to him in a very human, relatable way. Sae's also very engaging, obviously. (As well as being innocently freaky.)
Would I recommend this show? Yes, if you're up for this kind of thing, but watch out for Phase Three. I might even suggest stopping in the mid-thirties. You'd be skipping some stuff that's worthwhile, but it's outweighed by dull material that's clearly weaker than the other shows you could be watching instead. Everything's anime-original by that point anyway, so you could tell yourself it's not canon and make a plan to read the manga. However when the show's good, it's good. It has funny jokes, lively characters and a storyline that (for a while) doesn't get bogged down in battles. I enjoyed it.