This — to me — is a rare gem indeed, because I can list only a single real flaw of it which I shall list upfront: some of the characterizations and interactions can feel a bit unnatural at times with how easily some characters come to enjoy each other's company despite starting out arguing; that is it.

Now onto what is good: I'll be the first to say that I love traps, but hate transgender characters but I couldn't help but love this due to the complexity and nuance to it all. One of the main characters definitely suffers from some form of gender dysphoria, and another of the main characters in much the same way is struggling with a desire to conform to gendered expectations after having defied them for so long, but these characters are given a reason for this, a backstory, and a nuance where the world isn't filled with absolutes. Many of the characters in this story do things that many would find abhorrent, but there are few simple villains, and they are all given a history, and a set of reasons wherefore they might do these things.

The story mostly focuses on three main characters with one semi-main character and a lot of side characters that exist for the benefit of the four primary characters but are really not as fleshed out. All characters are 19 years old at the start of university.

Yuki:

Yuki starts the story a trap; he's biologically female but so masculine in appearance and acting that most mistake him for being male; Outwardly Yuki loves this but secretly Yuki actually despises this and wishes to be more feminine. He actually loved being boyish as a child but later it became "his thing" to such an extend that he feared doing something else when growing tired of it. He feels he wasted his teenage years being this boyish and one of his few feminine moments is masturbating in an old female school uniform.

Mikako:

Mikako is a female with the reputation of a rich, innocent legal loli with perfect manners who in fact hides a secret of being an extreme misandrist that paradoxically also works as a prostitute to fund his rich appearance and despises the many males he otherwise enjoys having sex with and seems to have troubles getting aroused if he not hate his sexual partner. Mikako whilst being 19 continues to tell all clients that he's actually 15 and hates the idea that there will be a time where this lie will no longer be believable.

Kaito:

Kaito is a male with a reputation of good looks and flirtatiousness that has a string of older, rich female lovers that pay for his expenses but harbors a secret hobby of crossdressing. He is coming to terms with the problem that as the years come and he is losing his teenage androgyny it takes more and more effort for him to convincingly pass as female; what started for him as a childhood hobby consumes him more and more and he's beginning to show signs of actual gender dysphoria where crossdressing is not enough and he wants to actually become female.

Syou:

The childhood friend of Yuki who is one of the reasons Yuki felt trapped in adopting his boyish persona whom Yuki now feels trapped by and finds somewhat suffocating. This character is not as important and more rarely featured than the other three but is very instrumental at enabling many elements of the plot.

Hence the title: the three leads have some connexion to being nineteen years old and finding some solace from being in a female school uniform. It's about these three characters and how their lives intertwine and affect each other — at first, they do not even know each other all the while influencing and affecting each other until a complex web of emotions of love, friendship, and lust develops between them with each of them helping, and destroying each other along the way.

The nuance of most of these characters is splendorous — in particular I said I dislike transgender characters, yet love traps because traps to me repræsent freedom and transgenders conformance, but Kaito's gender dysphoria is crafted in a very dimensional way. It's not a simple story of "I feel female; I have always known this; therefore I must conform to female social expectations.", but the audience is invited through flashbacks and dreams into Kaito's past that explains how Kaito's obsession with being the perfect female came to be — the character's own love–hate relationship with his penis is also one of wonderful dimension.

Plot-wise there is no filler whatsoever; this is actually 100 chapters sans any filler: no chapter can be missed for the story to still makes sense which continually progresses and has a fitting conclusion.

Thematically, it deals with violence, rape, co-dependence, infidelity, lies, insecurity, gender dysphoria, prostitution, and very complex emotions that defy normal expectations. Rapists and borderline-murderers are humanized and develop themselves; friends get into extreme arguments about betrayal and make up again.

The emotions are as said quite complicated; it isn't a simple case of "I love you and therefore want to be in a relationship with you, have sex, and start a family.": one character in particular has a madonna–whore complex and cannot bring himself to have sex with the object of his love as that would defile the latter and is obsessed with keeping him pure.

It reminds me in many ways about the thematic elements of Uwa-Koi, but the execution is superior in almost every, and Uwa-Koi is one of my favorite works. Uwa-Koi had some flaws in terms of pacing, and unrealistic harems as well a too much of a self-inserty lead character without agency; this has none of that.