A 24-year-old English teacher who teaches at Kumaneko High School, Kazuma is described as a "plain, glasses-wearing English teacher." Kazuma is the only one who looks for Fumino when she runs away and ends up marrying her, supposedly only to help her and Teppei. He is sometimes goofy and says he appreciates seeing Fumino's rare smile.
He asks Fumino to help him with problematic students, although he is a teacher. He has a calm and caring demeanor and cares for young Teppei more than Fumino does (according to her). He often gives Teppei candy for his hard work or just for being cute. Kazuma cooks for the family and usually sleeps much later than the rest of his family because of his dedication to teaching. Kazuma have numerous amounts of costumes for both Teppei and Fumino to wear and often dress them up for cosplay.
Even though they are married, they sleep separately. He occasionally sleeps in Fumino's room, but only next to Teppei. Kazuma isn't open about his past, but later in the story, it is revealed that Kazuma was once in a gang. According to his old "gang" friends, he was called Jigoku no Mā-kun (地獄のまーくん ?, Mā-kun from Hell) because he beat up 100 motorcycle gang members without getting a single scratch.
He still has formidable fighting abilities; shown when he beat up two guys with one hand, while with his other hand he was holding Fumino. He sadly mentions once that his family is still alive, only that they reject him because of his delinquent past. His mother has passed away. His father is an politician as revealed by Shōma.
According to Shōma, Kazuma was an excellent student, as expected from a person set to become the successor of his father. However, suddenly one day, he turned into a delinquent and left home.
Kazuma also mentions that he would like to tease Fumino first before "touching" her and very much does so every chapter. He feels that their marriage is only for Teppei's sake and that he shouldn't be "touching" her in case she leaves him for another man; which he would respect if she did leave him. Even so, he starts developing feelings for Fumino slowly.
He joked that if they were to sleep together, she would have at least grown her breasts to a size C. His birthday is on November 22nd.