A note before dissecting this terrible piece of work to its core, it might be the case that I am desensitized to works like this already, so I will not discount the feelings of others less experienced in the realm of "fucked up" manga, but seriously, this manga did not make anyone cry for a week as some may lead you to believe. I am of course not flexing my "hard stomach" here, this is just to give context and to not invalidate other people's experiences too much.
The paneling and composition
Already in the first couple pages of this manga, the reader is presented with some of the most confusing to read pages of any professionally published manga. I will not name any names, but it is certainly even worse than a particular "dark fantasy" manga which reigns supreme in the MAL rankings. The author clearly does not have the reader in mind when writing and drawing this manga, and as we will get to later in this review, avoids this with more aspects of his work. A good mangaka guides the reader's eyes where they want them to go, in every single page. This involves exploiting the page's composition, paneling, and the placement of text bubbles. You want to give the reader a smooth reading experience that never removes them from the immersion of the work you want them to read. "Metamorphosis" certainly fails at this. The only rule the paneling here follows is moving the reader's eyes from the top-right to bottom-left of the page, everything in between is up to the reader's intuition and guesswork. In several cases, one is greeted with character cutouts that transcend panel borders and disrupt the flow of the panel in every way, as the full-body cutouts aren't properly implemented. A good example I can think of is on page 31 of the full work, the reader has to guess which order the speech bubbles are supposed to be read in, as they do not match the standard reading order found in most other manga. A good example of a full-body character cutout is from "One Piece" when Yamato takes off their mask. Having a good flow to your page is one of the bare minimum essentials of making a good comic, and is a rule all comic-book authors and mangaka abide by, except for the author of "Metamorphosis", apparently.
A side note
Why is it worth dissecting and criticizing a hentai like this? I would agree, it is indeed stupid and an obvious low hanging fruit to overanalyze hentai in the same way one would analyze respectable works, however, the manga tries to be more than a simple hentai, so I will treat it as such, even though it fails miserably in what it tries to be. In addition, the majority audience reception of this manga is one that gives the impression that this manga IS in fact something to be taken seriously.
The characters, character arcs, writing, and pacing
This manga is not a good example of what most uninformed individuals would refer to as "character development". Why might that be? The girl clearly changes drastically throughout the story in reaction to her experiences. Yes, there is the PRESENCE of a character arc in this manga, but in the same way as some certain story about man-eating giants attacking humanity hiding behind walls, it is not a good character arc. This is for two simple reasons: the character progression is too fast paced, and that there is zero prior character development (character development meaning the actual WRITING of the character, not the process of change they go through) before she begins to change and bad things begin to happen to her. Why should any reader care about what happens to poor Saki-chan? Any 3 year old could write a story with a character who has a lot of bad things happen to them. Here, I can write one now: 'there is an 80 year old grandma who is nice to her grandkids and she gets murdered on the street because people are bad. The end'. No one cares about that grandma for any reason beyond basic human empathy, as the only empathy she generates is through her existence as, one, a human, and two, as an elderly person. Nothing in that story I just created gives reason for anyone to care about her. This is the same for "Metamorphosis". There is no prerequisite for the reader to care about Saki-chan, or anything that happens to her, besides the fact that she is a fellow human, and a seemingly innocent girl who just wants to fit in (something lazy authors use to write easily relatable characters if they don't actually feel like writing a fully fleshed character profile).
Now for the pacing. Characters here just make decisions on a whim just to fit the narrative. "Oh, we just heard a rumor that Saki-chan is having sex with the boys in class? Let's all hate her without further notice! The author needs her to be alienated from her social circle and to apparently suffer more!", "Oh, I'm pregnant again! I will not abort the baby this time because I do not want to go through 'that' again." Now in this case, because we never actually saw "that", the reader is left to assume that she doesn't want to abort her baby this time because it would... hurt? Who knows. This decision is a turning point in her character arc and it is sudden without any form of buildup to it. Characters just change and react in accordance with what is required for the story. This is lazy writing, and the result is a main character who gives zero reason for anyone to invest any sort of emotional investment in them. Unless, of course, the reader is one of the many people who take characters at face value and relate and invest time into them on the basis of their mere existence as people, rather than doing it for any solid reasons like relatable character traits, decisions, or impactful actions in the story.
Saki-chan is also another example of terrible female writing by a male author. The author writes women as they exist in his head, there to satisfy his fantasies. Girls like this don't exist. And even in a work of fiction such as this, it is offensive to the reader to even portray a character so stupid with actions and decisions solely based on his male fantasy, and expect the reader to actually feel something for them. Now of course, it is a given that women in hentai manga are not realistic, and this goes without saying. But I happened to be unlucky enough to come across fans of this manga praising it for being "realistic", so excuse me.
Also, just a last note for the writing, this manga was insanely predictable. Now this may be an obvious case for hentai manga or erotic works in general, but this really stands out as it isn't even predictable in an absurd sense, it tries to actually portray itself as a solid story with shocking twists and turns.
It fails as a story, so how does it stack up as a hentai?
To cut it short, it fails as a hentai too. I will not try to boast, but this is one of the most visually mild hentai I've ever read. Most of this aspect of the manga comes down to each individual's taste, but people shouldn't waste their time on this manga if they want a good hentai to satisfy their business. It is stale and lacks creativity. Even in the subgenre of "ugly bastard" or "old man", something I dislike to begin with, there isn't anything noteworthy or new in this manga. I would rate the hentai aspect of this manga a 4/10, as there were a few good panels.
So then why isn't it a complete 1/10?
It certainly almost is. But the way the author draws male testicles is nice, and some of the tragic things that happened to poor Saki-chan near the end were definitely kind of infuriating, so I guess the author got me there. But this impact lasted until the second after I read the last page, so as far as an impactful read, it was quite weak.
Conclusion
"Metamorphosis" is truly one of the most overrated manga and hentai I've ever come across. The fact that it has over 40000 members on MAL proves just how easily impressionable tiktok teens are, with the slightly unsettling experiences Saki-chan goes through being an easily advertisable set of events that strike the interests of normies on the internet whose tastes are shaped by the instagram, tiktok, or youtube algorithms. The manga fails as both a story and as a hentai, and is a waste of time for anyone beyond the mental age of 12 looking for something impactful to read or something to satisfy their hentai business.
