I will spoil some beats of Shounen no Abyss here, as well as Aku no Hana. Be warned.

I must say, when I first found this title my interest was piqued. The art-style seemed pleasant, capturing atmosphere through paneling and shading akin to Shuzo Oshimi, as well as having a character design strikingly similar to Aku no Hana's post time-skip Kasuga. I must say I am a big fan of Aku no Hana, and upon writing this review, I have not read anything that quite captures atmospheric depression and loneliness in the same manner. So yes, I was excited to read something which could capture a similar feeling.
But as I continued to read Shounen no Abyss, the more it felt lacking, to the point where it would be frustrating. I suppose my expectations should've been lower...

The story follows Reiji, a seemingly normal high-schooler with normal problems who lives in the middle of nowhere. He gets lightly bullied by an old friend, has some family problems, and wants to leave town, but it's hard to tell if any of these issues really get to him at all, or if he's simply good at brushing them off. Instead, he choses to indulge in Idol culture and hang out with his friend. He seems happy. Then he meets his favorite idol who now works at a drug store and suddenly his everyday life is turned upside down... Does this sound familiar?

Already, I was inclined to make comparisons to Oshimi's Aku no Hana simply because of the artwork and Reiji being a Kasuga look-alike, yet so many story beats, atmospheric panels, and early moments feel so Oshimi it made me think that he was a main inspiration.
Boring town, check, normal but quiet boy with not many friends, check, girl who comes in and changes the way he sees his everyday life, check. But the difference between Shounen no Abyss and Aku no Hana become clear after these first few chapters end.

One main issue I see with Shounen no Abyss is that it fails to really capture WHY people become mentally ill. Reiji is fine one moment, then is trying to commit suicide the next. There is no flow, no development, no character beats that would lead up to this. There were some issues in his life, but there was no reaction to any of them. It makes Reiji seem shallow, a husk of a character that the author can manipulate into feeling any way he wants.
If I could bring up Aku no Hana one more time, the timeskip is a foil. We SEE Kasuga slowly becoming disillusioned with life for 6 volumes, then after the failed suicide, he has to crawl out of this mess himself. It's slow, and natural, and we can see how the events have shaped him post-timeskip. Reiji lacks any progression in his actions. We barely get to know how he thinks and reacts to things before he decides to end it all. Once again, this seems shallow.

The structure is the second big problem. Shounen no Abyss wants to have it's cake and eat it too. Have a cast of 'developed' depressed people, and have Reiji get laid by as many girls as possible. The idol he looked up to, his teacher, his best friend, his mother(?). These girls aren't characters, they are tropes that Reiji can use for sex and then move on to the next girl. It's almost structured like an arc, except there isn't any conclusion. Reiji goes from girl to girl without much of a reaction. And though we seem to be getting consequences from this, who cares? Why should we care when Reiji doesn't?

Pure and simple, I described it once as depression porn, and I stick to that claim. There is nothing that is being said here that hasn't been said better anywhere else, if it's saying anything at all. It seems like a pre-teen's idea of what depression would be like, adding in a bunch of cute girls to keep the attention of it's readers. It's begging to be called deep without putting the work in, begging to be labeled as a masterpiece without any actual progression. Overall, Shounen no Abyss is not worth your time. It wasn't worth mine. There's nothing of substance here, and I doubt there ever will be.