The passing rapist in the anime.
In the novel, he was actually given a role in the story.
----------
It all starts at the beginning of the novel (4)--
After knifing out his bug, Iriya and Naoyuki were at a restaurant. After the authorities got too close, Naoyuki finds out about the empty school (that you see in the anime).
When they get to the school, Iriya creates the alarm devices. On the first night, a man enters the school grounds. As Iriya was asleep, Naoyuki took it into his hands to defend her. As the room was dark, Naoyuki didn't see to much of the man who entered the room they were in and attacked him while shouting. Because Naoyuki shouted, the man also shouted in surprise. Naoyuki stopped his lunge at the man, and Iriya woke up. After the lights were turned on, Naoyuki saw that the man was actually weaker than he first thought, and was currently in great shock at being attacked.
When things were cleared up, the man introduced himself as Yoshino. When Asaba asked him if he was a homeless, Yoshino replied that he was, though he actually did have a house, but haven't returned for 5 years.
Yoshino ends up cooking for Iriya and Naoyuki. A couple days later or so, Naoyuki asks Yoshino a "what-if" question. Naoyuki basically states Iriya's situation without using her name and asks what Yoshino what he would do.
Yoshino's reply was far more "deep" than Naoyuki thought, causing Naoyuki to ask Yoshino what his ex-profession was. Yoshino replied with rather pointless jobs. Naoyuki asks Yoshino what his ex-ex-profession was, and when he got the 4th "ex", Iriya came in and interrupted Yoshino's answer.
Yoshino then asked the two to play with him a bit. They would have class, with Yoshino as the teacher and the other two as the students. Yoshino had been a Japanese history teacher (not explicitly stated). At first, Yoshino, not having taught for so long, used only books to teach the class and it was boring. After a while, Yoshino began to teach class his own way, and Iriya and Naoyuki became absorbed into the class.
And so, a week would pass.
Naoyuki cuts Yoshino's hair. Yoshino goes to the library for books for reference for class while Naoyuki goes shopping. At the library, Yoshino overhears the librarians talking about how "there was a white-haired girl in the abandoned school building and that police might come soon".
Yoshino checks out some books. After he leaves, he throws those books away, pulls out a cigarette, and says "it was a good dream".
Meanwhile, Asaba buys what he needs. As he leaves the store, he finds porn on the ground... -_-
Yoshino goes back to the school and finds his rucksack. Iriya was staring at him. Yoshino imagines himself making a dash to escape.
Then, while cleaning his pe***, he imagined what was next.
Yoshino goes out of the door to leave, but is grabbed by Iriya, who tells him to wait until Naoyuki comes back. Yoshino knocks her back. This causes her to snap and attack him. He gets pissed off and starts to attack her. Afraid, she runs to the storage room (I think that was it). Before she could close the door, Yoshino manages to get inside. He starts to "attack" her. Then he felt the orbs on her wrist. Iriya takes this chance to stab him.
By the way, while this was happening, Naoyuki was pleasuring himself with the porn he found and his hands... -_-
After finishing what he was doing, he realized an elementary school girl was looking at him. This was Hikari Itou (no, not Makoto Itou), a girl who could be described as a "problem child". Naoyuki had his zipper still open.
She screams and chases him (later labeling him as "hentai-yarou") and throws a dango at his back.
Naoyuki gets back to the school and zips up his zipper. He sees Yoshino limping out of the school and walks away. Naoyuki later finds Iriya at the storage room. Putting everything together, he realized what had happened.
Naoyuki gets REALLY angry. He grabs a bat and chases after Yoshino. In his mind, he was thinking stuff like, "when I find him, I'll show him no mercy" and "too bad if he doesn't die from the first swing" and other extremely violent stuff like that.
But he could run anymore, and starts to cry.
Hikari finds him again and slowly approaches him. Apparently, she believes a lot of what her mother tells her, but lets put that aside. After a rather "meh-level" conversation, she said something to Naoyuki that she had heard her mother say that was apparently a devastating weapon against males. Naoyuki gets up, gives her the bat, and walks away.
Yoshino had walked to a telephone booth and reported Iriya and Naoyuki. He had stolen all of their money.
When the police come, Naoyuki and Iriya escape. Naoyuki finds the cat, coaxes it to follow him with cat food, and Iriya and Naoyuki walk along the railroad.
Naoyuki finally shouts at Iriya. Like the anime, she snaps or as the novel goes:
"hakai" or "destroyed".
Her reaction was a bit more extreme in the novel. She started to "claw" at her hair, causing her hair to start falling, and Naoyuki tries to grab her with his hand, which caused her to slice his hand.