Toshiyuki Karasawa/Relationships

Motoharu
Karasawa is good friends with Motoharu. They are classmates as well as colleagues in the Student Council. They both have a strong sense of duty and a natural inclination to help others out. Motoharu believes that they should learn to decline others’ requests once in a while, but Karasawa objects to this. However, Motoharu was pleased when Toshiyuki charged for their services.

After school, they sometimes walk back together, and even have role-plays of their own much like those of the main trio. Whenever Ringo barges into North High, the two of them and the Vice President try to prevent her from harassing them or tease her in turn.

Habara
The two share a lot of history between them. In elementary school, Habara terrorized kids as the Archdemon and Karasawa was genuinely frightened of her. She has been shown bossing him around, and his most traumatic childhood memory is of her hitting him in the middle of his forehead with a stick. This left him bleeding and a permanent scar remained behind, which he now covers with his cap.

Now teenagers, she feels guilt over her past actions and tries to make amends. This is best shown when Habara sees his head scar when he shows it to Ikushima and Yanagin, causing her to feel guilty. She tries to apologize, but he doesn't accept it and she ends up attempting to pay 5000 yen for his forgiveness.

It is shown that in spite of adopting a stoic side, Karasawa continues to be scared of her in high school, despite her changed personality. He takes a variety of precautions whenever she is in the vicinity - this includes clutching a sharp pen in his pocket if she touches him, spraying an anti-bacterial on things she returns to him, and somehow sensing her presence if she approaches from behind, among others. This makes him seem paranoid, but she bizarrely interprets it as him having feelings for her and perhaps being shy. It is also hinted that she has feelings for him.

After saving him from a fall at the end of the series, Habara ends up getting injured in his place. After this, she believes she's made up for the scar, forfeiting her timid nature and appearing confident in Karasawa’s presence. This transformation of hers makes him deathly scared and he sweats profusely.

Tadakuni's younger sister
Tadakuni’s younger sister seems to have a crush on Karasawa. When asked whom among her brother’s friends she would like to date, she answers with his name, although she attacks him immediately afterwards when he makes a lewd comment. Karasawa becomes scared and attempts to hold her off. Later, she becomes interested in seeing his face without his cap, but becomes dismayed with the result after succeeding.

She calls upon him at North High later, asking him for help after getting into a fight with a boy at her school. Telling him that he was the only one she could rely on, she is let down by his response and leaves to sort it out herself. He ends up following her to make sure she was safe, even though she is shown to be stronger than he is.

Ikushima and Yanagin
Karasawa occasionally interacts with the two of them, since they hang out frequently at Habara’s house which is next door to his. They sometimes try to harass him based on their notions of being superior to high school boys, which he resents. He’s able to distract them with chocolates and quiet them down by showing them his facial scar. This leaves them apologizing, although neither of them were directly involved in the incident but most likely feel bad for his past pain. Karasawa shares Ikushima’s view that Yanagin is often too brash and vulgar, even telling her directly that many of her male friends thought her insensitive. He and Yanagin are also childhood friends and went to the same elementary school. Yanagin took part in the fight against the Archdemon mainly to avenge his injury.

At the end of the series, the two notice Habara’s change in personality. Yanagin seems relieved, but Ikushima notices Karasawa’s reaction and remarks that it seemed an unhappy ending.

Other
Karasawa has been shown hanging out with the main trio a number of times, mainly during their summer vacation. Initially, their extended group featured him and Motoharu, but he appears less later on, and others like Mitsuo, Megane and Chapatsu feature more in the group.

The Vice President and Karasawa are on good terms. They are very similar in their diligence and hardwork, and the VP is impressed by Karasawa’s sharpness and presence of mind. The two and Motoharu look on Ringo as an air-headed friend, yet a nuisance, and try to distract her whenever she makes it to the Student Council room uninvited.

Takahiro and Karasawa are friends who sometimes walk back together after school. They went to the same elementary school, and as such are aware of the threat of Habara. Takahiro knows of (and is startled by) the existence of several scars on Karasawa's body.

Karasawa is also acquainted with Habara’s and Yanagin’s seniors, although he isn’t on very good terms with them. It is indicated that two of his scars are due to their doing. Like Habara, they feel guilty when he shows them his scars and apologize profusely while attempting to make amends.