Long story short: bully boy have grown up and now must face the consequences of his acts during his childhood school life. Simply put, a beautiful story about forgiveness, redemption, love, friendship, and maturing. Now, let's go to a more elaborate view on this masterpiece.

First of all, I have a very strong bias towards bullying/redemption stories, and I don't plan (even remotely) to pretend this is not biased. After all, my reviews are based on my life experiences and personal tastes about the things I read and watch. And talking about redemption stories, this is all this manga is about, and it's one of the best redemption stories I've ever seen in my entire life.

The premise: Shouya is your average elementary schooler: mischievous and lazy boy, always playing and messing around with his friends and classmates and, well, just being a kid. Everything changes when a new classmate, Shouko, arrives at school. She could be just another new girl at school if it wasn't for a simple detail: she's deaf. And, as you would expect from your average chaotic kid, Shouya takes advantage of her disability. Starting with dumb pranks, things start to escalate to the point where Shouko is not only socially excluded, but also physically hurt by most of her classmates' bullying. After the commotion, Shouko changes school and the responsibility must fall on someone's shoulder. Even if the bully came from a lot of kids, and with the knowledge (and non-interference) from the teacher, it all falls on Shouya's shoulders. Now, betrayed by his friends and classmates, he is the one being bullied and like Shouko, without anyone to rely on.
Fast forward some years and now we have a teenager Shouya. An awkward, quiet, depressed, and socially excluded boy without any friends or aspirations. The only way out of everything that he's done, from what he sees, is suicide. But before killing himself, now that he's a more mature, empathetic and sensible human being, Shouya wants to find Shouko and apologize for everything that he's done to her and the hell that he made the poor deaf girl live in when they were just children and he had no notion of the consequences of his acts.
He learned a bit of sign language just so he could apologize to her properly and show how he regrets his bullying. And after finding her, without not even knowing the reason, in a scene that is one of the most beautiful scenes of any redemption story you'll ever read, he asks: "Can we be friends?".

As the story progresses, you understand not why he bullied a disabled girl (which is irrelevant, he was just a dumb mean boy doing dumb mean things) but the effects that it had not only on her mind but on his as well, how much that made both of them suffer and how it affected the way both of them saw the world, each with their distorted and sad way. You get to know other people involved directly and indirectly with the childhood bullying, people that regretted their acts as well and found their own way to cope with the feeling of guilt, people that didn't regret AT ALL and were quite prideful for their acts (fuck you Ueno), and people that also suffered from bullying in their lives and also found coping mechanisms.

The way Shouya's guilt is portrayed and described is so real that you can relate to him even if you never suffered from bullying or practiced it, and how he is reluctant to accept that happiness can come for him too even after all that he's done is sad and also inspiring in a lot of ways.

Concluding, a wonderful story that makes the Supreme Master of Redemption Zuko proud and even people not familiarized with manga should read it.