And yeah there is an anime for this. Its really old tho, it was made back in 2006 and although the budget was probably sizable back then, today the animation has not aged all that well. Anyway, this manga is based off the anime which is actually based off of a light novel series (which is surprisingly still continuing based on the wikipedia page o.o). I've been looking for up to date translations of the light novel where the anime left off so if anyone knows a site that has them, hit me up plz. But back to the review, the manga is a super incomplete quickie adapation of the anime. Its less of a manga in its own right and more like a glorified doujinshi. I'll admit tho, the art is really cute and resembles the art used in the light novel's cover. I'd recommend watching the anime because it really is a great story. Its sweet and heart wrenching and all of the characters are interesting. I just wish that some of the other familiars could have had more fleshed out backgrounds but theres only 24 episodes and a crap ton of plot to cover, so thats understandable. Definitely recommend!
SPOLERS AHEAD Edit: More indpeth about the story and anime tho, at times the animation can look kinda jank. You can tell that they really had to stretch that budget to make it last 24 episodes. It can look decent in places where its supposed to but it also seems like they really had to stick in weird long pauses so they wouldnt have to animate some scenes lol. It doesn't look like much at first, the character designs for some of the shikigami are kinda generic and almost all of the human character's faces and designs look the same. The characters themselves are what really carry the anime. And by characters I mean Seimei, Masahiro, and Touda. Everyone else is kinda in the background and pop up to help out those three and then poof away. The shikigami seemed like they had so much more potential to be fleshed out into amazing characters and I'm hoping that the novel follows through with that but in the anime, they're just kinda there. One gripe I do have about the story both in the anime and in the few light novel chapters that were translated is that Akiko is such a bland character. Its like she was made only to be Masahiro's generic love interest. Which, in all honesty is probably what the author actually thought but I kinda wish there was a reason for us to root for her romance or even give a damn whether or not she died. She shows up in the anime fairly often but whenever she's on screen she's only there so a) she can be rescued by masahiro or b) she can motivate masahiro. Their relationship doesn't progress all that much in the anime and her role remains a static damsel in distress plot device. I kinda wanted them to at least have more indepth conversations or to bring up how she's a princess so she can't marry him and to have them deal with that road block seriously but they dont. In fact, that whole event was used as a way to further explain/develop Guren and Masahiro's relationship lol. No joke, Mokkun shows up on Seimei's balcony after Masahiro's angstiness and explains how although he doesn't care much about human politics, he wishes that he could tear it all down (implying that he wanted to do this so that Masahiro could be with the girl who he loved). Akiko doesn't really get that much characterization or character development otherwise. In fact, her entire character can be summed up in one word: kind. That's a great character trait to have and all but its the only thing that defines her and unfortunately she's kind of forgettable. Honestly even Twilight's Bella Swan has more character than Akiko does, and thats saying something -_-. On the other hand, Masahiro and Guren's relationship was really fleshed out in the anime and even more so in the later light novel chapters. Like, holy shit they got so much development. One of the things that makes Shounen Onmyouji stand out to me after all this time is that it was the first anime that i ever watched where you couldn't pass of the two dude's relatioship as bromance or subtext. Nah, fam its straight up love. Not the kind of love you think tho. Its not the aishiteru, sexy time, yaoi, shounen ai love. Its platonic family love. Like the kind of love an older brother/father/grandpa has; a guardianship kind of love. Its blindingly pure (not that that stopped me from shipping guren and masahiro lol) and really obvious in both the novel and the anime. For real, they slap you in the face with it every episode. Its one of the most well done relationships I've seen (at least between two dudes). The author dumps it on you in both subtle and overt ways. There are moments where its obvious, like when Masahiro tries to sacrifice himself so that Guren can escape Kyuuki or when Guren goes beserk when Masahiro gets stabbed by a possessed Akiko. But they also show their love in real subtle ways. Like, Guren doesn't need to explicitly say that he cares about Masahiro (although he also does this) or vice versa. You can already interpret that from their actions. Theres a moment in episode 2 or 3 I think where they're fighting goetsu and the Ox monster demands a human sacrifice and Masahiro instinctively grabs on to Guren's claw hands. The way Mokkun cuddles up with Masahiro randomly. The head pats. The teasing. The way Guren only lets Masahiro call him by that name. The freaking protectiveness. He's not just protective of Masahiro like he's some helpless kiddo tho. He also encourages him to do his best to become and onmyouji and to fight his own battles. Its honestly the sweetest thing ever. I don't wanna spoil too much of it because I want u guys to watch this show. But seriosly this anime gets 10/10 from me for those two alone. They're so freaking great. I can't even. I wish someone would finish translating the light novels tho, because it goes up to 44 volumes. 44 volumes of epic bro-love.