Awesome Music: The film's soundtrack, composed by Kensuke Ushio, combines instrumental and electronic sounds for unique pieces that not only heighten the film's quieter scenes, but really speak to the characters' headspaces. Special mentions go to "frc", which plays during Shoko's attempted suicide and gets more chaotic and panicked as it goes; "btf", a melancholy piece during the funeral of Shoko and Yuzuru's grandmother that glitches and fades while still being peaceful; and "lit (var)", the film's closing piece, which starts out simple before basically exploding as all the X's fall from people's faces and Shoya breaks down.
Base-Breaking Character: Shouya. He's not scrappy material, but there is a segment of readers who can't sympathize with him after his bullying of Shouko in elementary school. This is dependent on the reader believing his character development and attempts to make amends afterward don't make up for what he did as a kid.
The POV chapters following Shouya's coma. While some like that these chapters shed some light on Shouya's friends, others felt that the story was more interesting when it followed Shouya's POV.
The manga ending. Some people found it like the perfect cap to a very emotional story. Others found it severely lacking since it doesn't give a resolution to any character.
For completely unrelated reasons there was debate of whether in the final chapter Shimada was living as a woman and dating Keisuke Hirose, considering a female character looked a lot like him. It's generally considered to be due to the art style rather than intentional.
The news that the manga would get a movie instead of a 12-Episode Anime was met with mixed reception. There were worries about how they would fit the entire series into an under-120-minute film, or whether they would just focus on the elementary portion. Other fans were just elated for an adaptation. Once the film came out, while it received critical acclaim, some fans thought it was at minimum a decent adaptation.
The movie being done by Kyoto Animation was met with disdain and joy from fans. It often came down to a Fandom Rivalry with other studios that the fans would have preferred to animate it. There were also many fans who wanted a true-to-style adaptation and were scared that Kyoani would use one of their in-house art designs, which in themselves are criticized for being too similar looking. Other fans noted that the characters designs in the manga resemble Kyoani works and said it wouldn't be a huge leap in style. The film ended up using the manga designs rather than the typical "Kyoani style".
The ending of the film itself: To be specific, it ends during the school festival, when Shouya finally sees all the X's on everyone's faces, besides his friends and family, fall off. In the manga this sets up his new outlook on life and the changes in both his friends and his surroundings, but the movie makes it polarizing by both ending at that point, and changing it so that he is crying in the middle of the festival while the faces of certain people flash on the screen, ending on Shouko's face. To many, it comes off as rather anticlimactic after everything else that just happened.
Yuzuru calling out her mother for being so aloof and only trying to make amends when Shouko is already broken is quite satisfying.
Shouko's mother slapping up Ueno when the latter tries to beat up an injured Shouko is this in-universe — Ueno literally gets sense knocked into her about what she's done — and out of universe.
Crosses the Line Twice: Shouya having to earn 1.73 million yen (about 15,000 American dollars) to pay for damaging Shouko's hearing aids is karmic, especially since it takes him five years. His mother yelling at him for being suicidal after he gives her the money and confesses his plans is dramatic. Her burning the money by accident, right after he promises not to commit suicide if she doesn't burn it? A Funny Moment.
Die for Our Ship: Ueno suffered greatly from this in the first two-thirds of the story, but later this was prevented thanks to her only casual encounter with Shouya in the final of the manga and a strong Les Yay involving Sahara.
Ending Aversion: Given the obvious feelings of the main characters towards each other and the fact that most fans wanted to see them together, it's no surprise that so many were unhappy with the open end in the manga. The adaptation makes this more palatable, as it ends without being neckdeep in the film subplot, instead choosing to end on an optimistic note.
Shouko's grandmother. Being one of the few truly good supportive adults in the manga definitely helps.
Mashiba, who initially seemed very suspicious to most readers. Then, he stood up for a young girl being bullied and revealed that he too had been bullied as a kid. Then he threw water in Takeuchi's face. Needless to say people warmed up to him a lot.
Maria, Shouya's kid niece, is quite popular for being both a rare (half-)black character in anime/manga and being so cute.
Sahara, due to her generally easygoing and kind nature making her come off as a great friend and total (female) bro for Shouya and Shouko.
Fan-Preferred Couple: Shouko/Shouya, obviously. The fact the manga only hints it will become canon in the future, and that the film removes most of the romance, making Shouko's confession into a Big-Lipped Alligator Moment, makes fans' desire even stronger.
Funny Moments: Nagatsuka provides most of the humor in the series. On a meta level, he's even funnier since he looks like an older Steven Universe.
Shouko's mom once you find out what happened to her husband. Her in-laws blamed Shouko's deafness on her, claiming that she must have done something wrong, and pushed their son to divorce her because of it. Does not justify or forgive how she tends to treat or behave around her daughters, but it does add another dimension to her that wasn't previously seen.
Shouya, definitely. This poor guy's life is a roller coaster of feelings. As a child, while he wasn't the only student who bullied Shouko, he was the first and definitely the worst of them. His actions ranged from calling her names, to physical harm, to ruining her hearing aids. And he did all of this while feeling proud of himself and not thinking about the consequences of his actions. It all comes back to bite him though when his classmates and friends quickly threw him under the bus when the time came to fess up for Shouko's bullying, and soon he became the class scapegoat. Shouya spent his years through middle and high school without any friends or support because of this, and grew to disdain and distrust people so much, he started mentally x-ing out their faces just so he didn't have to deal with them. During this time, he was also hit hard with the guilt of what he did to Shouko. This guilt was so bad that he spent those lonely years working and trying to resolve himself, so that one day he can earn Shouko's forgiveness, and maybe even forgive himself. And since his reunion with Shouko, his life has just been filled with way too many emotional twists and turns to list. Seriously, someone give him a hug already.
Les Yay: Sahara seems to be a magnet for this. There's her groping Shouko after her reintroduction, her group of admiring kouhais, and her Vitriolic Best Buds relationship with Ueno. In the finale, Ueno shows off a ring that she received from someone asking to be her partner, someone 5'11", gorgeous, and starting their own label, who turns out to be Sahara.
Memetic Badass: Shouko's mom, who apparently has the ability to teleport and pimp slap those who have wronged her daughter.
Memetic Mutation: "Where is the healing?!", in reaction to the manga getting more and more depressing after Kawai's outburst.
Narm: As tragic as Shouya's fall is, it was hard for some readers not to snicker when the translation said that he suffered "major damage to his buttocks." Played up when Chapter 55 opens up with Ishida on his side while his doctors are examining the injury site.
Nishimiya's mother after Chapter 44. In short order, she apologizes to Ishida's mother over what happened to Shouya, ruthlessly beats up Ueno in defense of Shouko, then offers to pay for Ishida's hospital bill (although Ishida's family has insurance so it isn't necessary) and bonds with Ishida's mother over their ex-husbands. She's still a sharp and at times severe woman, but she's much more relatable than she used to be.
Ueno after Chapter 44 as well, when her own POV is shown that makes her more sympathetic, she finally admits to her faults, and ultimately makes peace with Shouko. The Les Yay she shares with Sahara also contributes to this.
Ueno earned this when on the Ferris wheel she tries to shift blame from herself to Shouko for Shouko's bullying and Shouya's loss of friends and current state, then responds to Shouko saying she hates herself with a slap and a flippant "so what". She is Rescued from the Scrappy Heap for many in later chapters of the manga, though.
Shouko's mother gets some flack for not letting Shouko use sign language in front of her, and seems to have no interest in wanting to learn it so she can communicate with her. Many people say she's a bit too authoritarian for her own good. She gets better after some defrosting. Possibly even Rescued from the Scrappy Heap after chapter 44, where she apologizes to Shouya's mother for Shouko causing Shouya's accident and slapping Ueno for hurting her daughter.
Given the revelations from chapter 45 to chapter 48, Ueno comes as slightly more sympathetic, given that she admits that she's aware of her personality issues; that she's a Clingy Jealous Girl and has a crush on Ishida, hence why she dislikes Shouko; and that she just doesn't know how to handle it. Compare with Kawai who is still in denial about her involvement in Shouko's bullying and manages to make Ishida's accident and Shouko's suffering be all about her. The fact that chapter 48's climax sets up a confrontation between Kawai and Ueno, the fandom was actually cheering for Ueno because Kawai comes across as the bigger Hate Sink due to her near-pathological It's All About Me/Never My Fault attitude.
Most people remember the scenes of the entire class bullying Shouko more than anything else from this manga. The anime makes the situation somewhat better by cutting many of the elementary school scenes.
Shouko's introduction—holding up her notebook, which says "I'm Deaf"—is the most iconic scene in the manga.
School Bullying Is Harmless is a bullshit trope. The fact that a group tried to prevent the publication of the manga because they didn't want attention brought to Japan's chronic bullying problem only drives this point home even more.
Similarly, the story takes a firm stance against the Pay Evil unto Evil trope. When Shouya receives the same kind of bullying and social isolation that he inflicted upon poor Shouko, it initially seems to be very well deserved... until we cut to the present day and see just how horribly this treatment has affected him, eventually reaching the point where Shouko blames herself for it happening to him and attempts to kill herself as a result. In the long run, Shouko's bully being given "poetic justice" for what he did to her only ended up hurting Shouko even more, and it's only through trying to understand and forgive each other that the characters manage to achieve any lasting peace.
Love isn't enough. You can love someone and still hurt them badly, even directly or indirectly. Shouko's mother believed Tough Love would help her daughter survive the school bullies, and the end result is Shouko is suicidal and Yuzuru spends most of her life cold to Mrs. Nishimiya, refusing to forgive her. Yuzuru tries to convince Shouko to not commit suicide by photographing dead animals, but all it does is make Shouko more depressed. Ueno always had a crush on Shouya but went along with bullying him as a child and blames Shouko when he tells her off for being a jerk as an adult.
Takeuchi-sensei, Shouko and Shouya's elementary school teacher and the shining example of Adults Are Useless, shows up when Shouya and Mashiba visit the school and he's just as shallow as ever. Which led to much rejoicing when Mashiba sprays him with his water bottle. Ishida mentally notes that he wished that he, instead of Mashiba, was the one who had sprayed with the water bottle, making the reaction In-Universe as well.
While the entire scene where Shouya essentially disowns his entire group of friends is a major Tear Jerker, more than a few people were glad to hear Shouya say exactly what the audience felt about Kawai.
Shouya:Kawai, you disgust me to the very bottom of my heart. Please don't say anything else.
A lot of fans cheered for Shouko's mom when she slapped Ueno in an effort to stop her from attacking Shouko, and kept on slapping her when Ueno just wouldn't stop insulting her daughter.
The treatment of the disabled may be shocking or even criminal to a lot of Western/European viewers (especially in an age of political correctness), but sadly the treatment of disabled people in Asian countries is much like this manga portrays. It is not uncommon for bullying and other malicious practices to be common towards the disabled, and little is done to stop it. This may count as a case of Deliberate Values Dissonance.
The movie's framing of bullying. While Shouya atones for his behaviour and admits he's done wrong, Ueno's viewpoint - that the bullying is Shouko's fault because she didn't fit in and dared to try to make friends in a school that didn't support her disability properly - is never really refuted by the narrative. Instead of everyone who bullied Shouko trying to make amends, only Shouya does, and the burden is put on Shouko to bring the group back together, with the bridge scene implying Shouya was wrong to try and force Ueno and Kawai in particular to face up to and make amends for their reprehensible actions. Not one person tells Shouko the fracturing of the group was not her fault. The movie shows that bullying is bad, but also suggests that keeping a group of people in harmony is more important than the feelings of any one person, so Shouko herself gets little catharsis.
After Shouko attempts suicide, she gets no help and is repeatedly scorned for her "selfish" attempt at killing herself.
Wangst: It's one thing to feel remorseful for one's cruel actions, but Shouya constantly beating himself up leads up to this.
Shouya's mother threatening to burn up the money her son earned, since they were several million yen in debt, and burning the money by accident anyway. Of course, considering the circumstances and the overall context behind the situation, her actions are arguably justified. Her son's life is definitely more precious than money.
Consequently, Shouya, by promising to compensate for the burned money, which basically boils down to him having to pay back his debt twice without any fault of his own.
Ueno beating up Shouko at the hospital in front of Shouko's mother. Who then starts to repeatedly slap Ueno to the point where they have to be separated, all while Ueno keeps badmouthing Shouko.
Takeuchi-sensei, who had ample opportunity to stop Shouko from being bullied, just to decide to not do anything at all.
The Woobie: Shouko, for being bullied in elementary school, which made her the way she is now.