Hiai Mousou feels like two good manga mixed into a slightly worse one.

TL;DR:Good yandere manga, but average for everything else, read it if you're into yanderes, or if you're into horror ecchi and don't have anything better

Hiai Mousou is a manga about the high-school teacher Kadomae Kazuma and the student Noeda Kanade, which kinda has a very big crush on him. The series starts as a relatively light-hearted ecchi comedy series about Kadomae trying to deal with Noeda while she constantly tries to seduce him. During this part of the series, the main appeal of it is mostly the ecchi, which sometimes is really close to straight up hentai, and the occasional glimpse at Noeda's completely yandere side, but after a certain point, the manga just goes full yandere-horror.

Both of the ecchi and the horror are really good and well executed, but the way the manga switches between the two of them feels really unnatural and almost makes the reader feel lost on what the manga is supposed to be like. This is a problem that could have been fixed if the manga had 5-10 more chapters at the middle that eased the transition to horror, but as it is now it feels kinda unfinished.

About the characters, i really love Noeda, in both the ecchi and horror parts, she really encapsulates everything i love about yandere characters, especially the way she gets crazier and crazier towards the end of the manga. Kadomae isn't really anything of note, he's kinda a dumbass and boring and, like all of the side characters, feels very pointless and like the only reason they exist is to give Noeda a reason to do what she does, instead of being actual characters.

The art is good, i particularly love the small details in it, like how the walls in Noeda's room get filled with more and more pictures of Kadomae every time we see it and how Noeda is always trying to hide the back of her hands so that Kadomae can't see the injuries on it from her father beating her, and the only time she doesn't is in a scene where it is in complete darkness, so it isn't visible. The way the characters are drawn is also pretty good, as well as the fan service.

In conclusion, Hiai Mousou is not a bad manga, in fact i quite like it, but the way it tries going from ecchi to horror is very bad and makes it feel confusing and way too sudden, the characters other than Noeda are very bland and forgettable, and the art, while not great, is enjoyable and with lots of details. It is worth reading if you're into ecchi horror and don't have anything better to read, and i'd say it's a must-read for fans of yanderes.