This whole review will be chock full of spoilers, otherwise I wouldn't be able to convey how unique and progressive this is for a manga- like wow.
Ignoring the whole "queer" topics I'm about to get into, as a horror/mystery manga, I'd just have to say it's good/decent (hence the 9 instead of 10).
You start to think that perhaps this will be a sort of detective story with a bunch of other smaller mysteries thrown in, but in reality they've only truly gone off topic once so far, which served as a huge turning point into Tetsuo and Amano's ideology, as well as being the defining characteristic of what makes this manga so great.
First of all, Tetsuo is a transgender man.
They introduce Tetsuo to you as a man, and once you find out as trans, they don't just write him off as a female, which I really appreciate.
They flesh out Tetsuo and his gender identity, and let the reader go on a journey of acceptance with Amano to come to with the fact that- yes, while Tetsuo has that banging female body that you'd without a doubt want to touch, he is a man, and you need to respect that above all else.
That's one of the main reasons I'm okay with the ecchi and exposing of Tetsuo's more feminine parts, we're supposed to keep in mind that Tetsuo is /super/ hot whether you view him as a male or female, but that our own lust (mainly Amanos) shouldn't cloud our judgement or disrespect the man that he is.
It also hit on a very important issue that I, as a trans man myself, struggled with, and have never seen a manga take on.
While Amano and Tetsuo are on the run, they come across this village, and while I'm writing this off as a spoiler, I don't want to get /too/ spoiler-y... So I'll just say that it gives Amano a larger respect for females and what they have to go through, as well as allows Tetsuo to realize that males can also like/feel things that are generally meant for "females" after Amano expresses his interest in it as well.
This is actually a rather huge block that a lot of trans guys face, being afraid of things that are too "girly" since it would denounce their status as a man in their mind, and Amano helps him get over that bump.
Amano himself struggles a bit with being a straight man who is not only attracted to a trans man, but restrains himself to only thinking of him as a friend out of respect for Tetsuo's sexuality, but also his newfound like(?) for crossdressing.
Basically, Amano is super open minded and kind, the kind of person everybody wishes they had in their life.
Amano believes in Tetsuo so completely, that even when Tetsuo gives up on himself
and pretends to just be a female, Amano still believes in the man that Tetsuo has proved himself to be again and again throughout the manga.
Edit::: P.S. I'm betting Amano and Tetsuo get together by the end- whether it be the two of them living as best friends or like... them dating despite them both being straight.
Am I the only one who thinks that?