Holy shit. That was oppressively dark, not to mention confusing as hell, but it's also an ambitious work of literature in manga form. It was nominated for the 2014 Diamond Gem Awards for the category Manga Trade Paperback of the Year.
It's set in at least two time zones, although I don't think there's any time travel. (I couldn't swear to it, though. There's a lot about this work that's abstract and enigmatic.) Ten years or so ago, some primary school children pushed their classmate down a well. Today, they're miserable, messed-up losers who probably aren't safe to be near. There's cruelty in both time zones, be it the near-psychotic thoughtlessness that's under the surface with children or else an adult who's simply let their life go to hell. You might have become a housewife and become a dead-eyed, miserable ghost of your former self. Maybe you're a loser in a dead-end job. Maybe you've simply gone mad. This is a world where nice, beautiful people don't exist. Even apparently likeable characters can turn around and shock you.
The art is realistic and ugly. These aren't stylised manga faces, but instead an assortment of unpleasant-looking real people. It's as if the manga-ka's going out of his way to demonstrate that Japanese faces look bad. The visual storytelling's also memorable, especially in its use of still frames and wordlessness. He can shock you, especially with his readiness to show the worst of human nature. A widowed father might have an erection when he's alone with his young daughter, for instance.
There's a surreal fantasy element, with butterflies. You'd probably want to read the book at least twice to feel you've got a grip on what the book's doing there.
This is the kind of work where the natural comparison points are literature, or at least SF. Vonnegut, Amis, David Lynch. That kind of thing. It's absolutely not fun. It's exploring the worst of human nature. The cruelty can be painful. If one child has a crush on another, don't expect the rejection to have the slightest shred of empathy. "You're gross and creepy." "You're ugly, so don't come near me." There's sexual content, but don't expect it to be happy and healthy.
There's a boy who'd like to attempt suicide again. There are people who hate themselves and people who should, but don't. Would you like to see the world destroyed? If so, your soulmate is here. A self-justifying bully can grow up to be a policeman. It's addressing the death of hope, self-worth and sanity. It's got people dissolving into clouds of glowing butterflies, then possibly becoming bloody splattered remains. (Maybe. I'll leave clarification of that as an exercise for the reader. There's a lot here that's never explained, or else suggesting enigmatic what-ifs and possibilities.) It's bleak, haunting and disturbing and I don't think I really understood it. I can't say it's not memorable, though.