Voiced by: Kōji Ishii (Japanese), Andy McAvin (English)
Kimura (木村先生, Kimura-sensei), also known as Mr. Kimura, is the only regular male character in the series. Kimura is a "creepy" and lecherous Classical Japanese teacher, who openly admits he became a teacher to be close to high-school girls. He is constantly lewd and openly seeks excuses to "observe" girls, such as during swimming class or when they are measured and weighed by the school nurse. He especially likes Kaorin, much to her dismay. His addressing her by her nickname "Kaorin" is inappropriate for a student-teacher relationship; he takes this a step further by asking her to address him by the similarly cutesy name "Kimurin".
Kimura habitually appears with his mouth gaping open, and his eyes cannot be seen behind his glasses. At his first appearance in the manga, Kimura seems normal, but takes on his usual expression after he was asked why he became a teacher—as if he had some sort of mental break. In the anime, he is always open-mouthed. Most female students (and some faculty) intensely loathe him, but some male students admire his "sincerity". Despite his lewd activities, outside of school Kimura appears as a responsible and kind-hearted person: he recycles littered cans, donates frequently to charities, and even offered ¥10,000 to a shrine as he prayed for world peace. He has a beautiful wife and daughter, who love him despite his strange obsession; his wife even claims to find him very handsome and thinks "he's cool!"
When Tomo finds a picture of his wife and asks who she is, he replies, in heavily accented English, "Mai waifu" ("Mein wife" in the English translation). "Mai waifu" has since become a catchphrase among male anime fans referring to a female character they find appealing.