Hajime Harada

Hajime Harada (referred to as Harada-sensei) is the homeroom teacher of Class D, and the PE teacher at Oto High School. Seeing as the school divides the classes based on students' grades, (meaning that class A students have the highest grades in the school and so on) he teaches the students who get the lowest grades. These students include Kako Motoya, Mikado Yaguchi, Jiro Nagakura and Heisuke Okami, who later on in the series transferred to another school.

Harada-sensei marries Heisuke's mother, Akari Okami, and the two have a son called Yuu-kun. They also end up adopting Yui Sendo into their family, once she and Akari patch up their relationship.

Appearance
Harada-sensei has short, black hair, an unshaved chin, and seems to always look at least a tiny bit worn-out or annoyed. He seems to be a tall man with a somewhat muscular build.

Personality
Harada-sensei is a somewhat grumpy teacher, with a no-nonsense attitude, but at the same time, he has been shown to be quite lenient with his students, as evidenced by Mikado and Kako's description of his test grading tendencies in Case. 16.

Background
Not much is known about Harada-sensei's background.

Akari Okami
Harada-sensei and Akari are quick to become infatuated with one another, much to Heisuke's dismay. He notes that Akari has a track record of falling for less-than-ideal men, but out of these men, Harada-sensei is clearly the most reasonable.

His students
Harada-sensei seems to share a good relationship with his students.

Trivia

 * As mentioned before, Mikado and Kako reveal in Case. 16 that his test grading tendencies are quite unique. The full context of this is that, according to Mikado, he would give her full marks on very lackluster answers to a question in which the students are supposed to give synonyms to a set of words (vexing, enthralling, etcetera). As answers to these questions, Mikado and Kako write "sick" on each, and elaborate by putting an action conveying emotion next to it (so, "sick [crying]" and "sick [laughing]"). Mikado could have been overexaggerating in this description, as it was her way of complaining that Kota was being too demanding, however, right after, Kako treats this as literal, and adds that "If [she draws] a real cool portrait of him on the back [of the test], he'll even give [her] bonus points." The image she has drawn on the back of the paper features a handsome Harada-sensei with sparkles, flowers and hearts around him, and a text which says "Harada-sensei is so cool!", which could be interpreted as Kako smooth talking better grades for herself, as she also put a +30 in the corner, indicating how many extra points she would get for the portrait (though that could also be an over exaggeration).
 * This leads to Kota thinking that the whole Oto High School is sick (weird).