[DeepL Translation - needs review] Volume 1 Introduction: Koichi, a senior in high school, has been having terrible trouble dreaming lately. Ever since he suffered an injury on his forehead nine years ago, he has been dragged into nightmares that are neither dreams nor reality. Jun, his younger brother, who is a self-confessed "black lover," can't help but be concerned about his brother's unstable condition. What in the world is happening to Koichi? The seal that has been placed on the broth...
A long-running atmospheric BL series
幻惑の鼓動 (幻惑 is given with the pronunciation やみ in this case) is a fairly long (30 volumes as of this review) dark fantasy BL manga series. It follows 天野 光一 (あまの こういち) right before the turn of the century as strange things begin to happen around him: he begins to see visions and have nightmares, and becomes entangled in the clan politics of four local families. And when I say "clan", think Fatal Frame-esque "these old families have some serious skeletons they're hiding" kind of thing. Volume 1 was published back in 1997 and just reached volume 30 in 2023, so strap in for a long ride if you decide to follow it.
Please be aware that this series does contain mature content; as far as I can recall nothing is explicitly shown on-page, but content warnings do include rape. This is also a bit of a slow-moving series; expect lots of build-up to certain events and for things to be vague for a long while. The authors are trying to build atmosphere, and while I think it's reasonably well-done, sometimes narrative flow gets sacrificed for it.
There is full furigana; the most difficult part of the reading process for me was either characters talking in slang and/or talking about poorly-defined topics (i.e. talking about someone or a concept we haven't been introduced to yet, or to a previous, off-screen conversation). This book also features a decent amount of "fantasy language": made-up terms are used to define specific mystical/magical concepts, and it may not be immediately obvious whether you're reading a "real word" or not. (I was saying thank goodness for the furigana there.)
The range of vocabulary (ignoring the slang) isn't necessarily particularly wide, but I believe the grammar touched N1 points at times. Honestly I'd recommend being a very solid intermediate, if not upper-intermediate learner before tackling this in full, if only to maximize your enjoyment and catch as much as you can.