The first half of the second episode (the final few pages of volume 1, chapter 1) shows us that Akito wasn't just some schoolyard troublemaker who was satisfied with disrupting his class. He was, in fact, a physically strong and openly cruel person who had no problem with going too far with his retaliation.
He has his goons capture their classmate, Mami. All of the boys then dropped her into a somewhat deep pond, with all of them surrounding her as Gomi kept pushing her head down with a broom. Even though the other boys were the ones who pushed her in there and Gomi was the one with the broom, Akito was the one who put them all up to it simply because she called him a monster. Never mind that she could have developed pneumonia or even drowned from this, it got so bad in the anime that he left Mami with a psychological scar that lasted several months later, long after he had apologized.
Akito initially knew that Sana would be too much for him to handle. However, Akito gets so irritated with Sana that he pushes her into a wall and chokes her. The impact when she hits the wall is metallic and loud. At this point, Akito's become so vile and unhinged that he's started to embrace his demonic behavior and has no problem with physically hurting Sana himself.
Tsuyoshi reveals to Sana that Akito has just been going too far lately, implying that Akito doesn't normally act this way. Anytime Tsuyoshi tries to reason with Akito, he ignores him, showing that his constant abuse by his sister sent him over the edge and the opportunity he's been given by blackmailing his teacher made him untouchable and unwilling to listen to anyone who won't cooperate with him. Not even Tsuyoshi, his best friend for years up to this point, could convince him to show some restraint.
There's also the issue that neither his sister nor his father knew how bad his behavior really was or that they, Natsumi in particular, are the ones that are helping fuel it. Just imagine if Akito had done something so terrible that he could have been expelled from school. How would that impact their view of him then and how would the affect the family?
Finally, there's also the knowledge that Miho Obana originally intended to have Akito carry a real gun to school. This is an eleven-year-old boy, and if everything he did in the published manga made him hard to redeem, imagine if he had that gun, especially in this day and age.
Anytime blood is shown in this series, there's usually a lot of it, especially in the anime.
Akito's hand bleeding hand after breaking the glass in front of his house was not something that anyone saw coming, especially in the anime, given the wacky and lighthearted tone that had been established at that point.
Fuyuki, Akito's father, suffers from an ulcer that has him faint on the table while eating dinner, with a stream of blood coming from what appears to be his mouth. Upon someone's first watch, it's easy to believe that he died.
Tsuyoshi's father throws a cabinet at Akito's face and his forehead bleeds in a creepily realistic manner.
The faces Kurosaki makes when scaring off Babbit range from unsettlingly funny to surprisingly chilling.
Sana's empty, lifeless expression caused by her Heroic BSoD after finding out that Akito is now dating Fuka. The amount of detail given to her eyes, along with the lack of white circles in her eyes, makes her look almost like a doll or a corpse, especially in the anime.
Similarly, Sana suffering from "Doll Syndrome" towards the end of the manga is terrifying, considering that the only physical symptom is an expressionless face. Everything else is related to emotional symptoms. It wasn't even the first time she caught the disease, and since there is no known cure, no one has to wonder why Misako went to the Mansion of Water filming location when Sana suddenly fell into depression after Akito told her he was dating Fuka.
Akito getting stabbed in the arm by Komori is unsurprisingly very disturbing. Two boys alone in the middle of the forest, with no cell phones or landmarks. Komori has a My God, What Have I Done? moment almost immediately after doing it, but Akito remains calm and unflinching. Then Akito pulls the knife out of his arm and Komori screams in fright as he starts gushing blood, to which Akito essentially responds, “Why are you acting like that? This is what happens when you stab someone”. Then he puts the knife in Komori’s hands and tries to direct the other boy to stab him in the heart while his left arm hangs immobile at his side still gushing blood. It should be noted that Akito (the victim) remains relatively calm during this scene, while Komori (the culprit) screams and panics.
