Specifics? Oh no! The exact follow up question I feared when I made my comment!
Well, here goes! Deep breath!
Spoilers
First the reader is presented with two possible outcomes, both are super bad for someone if not every one. With no quarter given to the “there must be some other way” train of thought the story has a kind of “if you’re expecting a happy ending you’re not paying attention” sorta vibe.
All the themes you warned of such as substance use, mental health issues, extreme trauma, suicidal/homicidal thoughts and the very idea of people that are afflicted by such holding the fate of every one else in their hands. (Mainly because that’s real life where I live.)
Next comes the idea of unending nose and ear bleeds! The tunnel, all the blood, vomit and such, I simply found text descriptions of these things to be more disturbing than VNs that rely on visual cues to portray this because my imagination does so much worse to me with descriptive words.
Lastly… Reuben! So much with this one alone! Innards! Licking said innards! The copious amount of times he said “and again” in the second bed time story! The first bedtime story! but mostly some of the views he expressed such as hostility towards an entire group of people despite many of those people must have been grown well after the events that he is resentful for. Also I feel specifically called out by a comment he made about docile people since that’s my natural disposition as a person.
Well that about wraps it up, and again I must emphasize that none of this is meant as criticism, with out such elements it would be difficult to write such a compelling story.
Ps. I like the way Neo is drawn and I hope to see more artwork of him beside the other characters. I know this might be difficult because the story is meant to be seen through his eyes so here is to me hoping for a mirror scene in the future!