Read this. Go back to the beginning and read it a second time. Then do the same thing again.
Why? Shounen Shoujo (not to be confused with other titles of the same name) (english "Little Boy and Little Girl") is a philosophical nosedive through discussions on death, killing, and individuality. Almost everything is metaphorical, and I doubt you will get 20% of the true meaning if you read through it too quickly.
On the story side, it is really well made and original, and it contains surprises every step of the way. Considering it comes from the writers of the Monogatari anime series, the themes go deep.
I'm not going to add any spoilers other than what is stated in the summary (also you might want to read the summary first for some parts of my review to make sense), which will be kind of hard since there are soo many things to be spoiled. Let's just get into the review.
As usual, I start from 5 (average) and add/subtract from that. I'm also going to refer to the two main characters with boy and girl, since the story never gives their real names.
If you are just looking for something nice to read while chilling and drinking tea in your bed, this is not for you. There is 0% fan service, 0% filler, and probably just 5% happy rom-com. The tags and the cover image are absolutely misleading. Drama: yes there is that, but not that much. Shounen: I guess, but the themes are pretty mature (just bc title has shounen it doesn't mean its for boys). School: like wth! Only the first chapter has a school, and the rest of the story is in a hospital-research facility hybrid place!
More appropriate tags would be psychological, tragedy, seinen, and a tad bit of horror and drama.
Again, this story has a lot to talk about death, killing, and individuality. From dreams to events to the very nature of the illness say something about those themes. I found myself contemplating on this soo much that I started an "arguement" with my friends about it (I hope they don't think I'm going to kill someone). [+2] I'm just going to give a tiny spoiler to one of the questions the story gives: "How many times can one kill before given the death penalty?" The question itself isn't much, but the way the author responds is genius.
Next is the setting. The basis of the story is very unique: Shounen has a disease which prevents you from seeing individuality, and at the same time he wants to be unique himself. The setting is used to its fullest throughout the story, explaining the themes and moving the plot. [+1]
The plot development is the next best thing. There are surprises every single chapter answering mysteries given and mysteries you didn't even know existed. I remember one point where I had an aha moment every time I flipped the page... [+1] Everything that is introduced is important to the plot. It is only 15 chapters / 3 volumes, but there is a lot of information fit into that. [+1] Though at times it does feel like it's going a bit too fast [-1]
Then there's the ending. The story reaches its climax with around 2-3 chapters left, and the last chapter is pretty slow-paced. I don't want to spoil too much... I'll just say I like those types of endings. [+1] You should also read the epilogue, since it discusses all the themes covered.
Character design is spot on! Though you can only see the faces of two characters, and they are children (I'd say its easier to put variety when drawing children), at least they aren't the default male/female faces. I guess I can't complain too much if the very theme is about individuality. [+1] The thing that really surprised me was that the artist even designed some faceless people. [+0.5] You'll see what I mean.
On the other side, background art is kind of plain. I guess you could say there isn't enough individuality... At least that's how the story justifies it. [-0.5]
There's also the symbolic side of a lot of the art, from the ink and cloth to the upside-down classroom. [+1] I won't spoil too much.
I also liked the more mature side of it. Even though it is about a little boy and little girl, the art of blood and pain is definitely a plus. [+1]
First, the initial character personalities are unique. [+1] There's a plain boy who really cares about being unique. Then there's a girl who is way too unique, who doesn't really care about life. The boy gets a lot more attention in terms of his personality, since he is the main character. The story goes into a lot of his psychology, like why he wants to kill the girl. [+1] That leaves the girl with more of a flat character. [+0.5-0.5]
The other side characters do play a significant role in the plot. They are okay, I guess. Of course there's the fact that everybody except two people have their faces covered, so you can't say much.
The character development is okay. The girl doesn't show that much, but the boy does show his change in thought process slowly. [+1]
The relationship between the boy and girl is the best part. You can see how they get close to each other, but also the outward happy friends appearance vs. their actual distrust and twisted relationship. [+1]