Hayato, normally referred to as Kamitani, is a student at Morinomiya Academy and son of the middle school science teacher, Shizuka. He is the second member of the babysitting club and a member of the baseball club. He is in the same class as Ryuuichi.
Hayato is tall and considered handsome by the girls in his class. He has short black hair and narrow eyes with light green irises, features he inherited from his mother, Shizuka. He is impassive and normally has a deadpan expression, conveying a stern and fierce expression only when he has strong feelings, especially when angry at his younger brother Taka.
He is quiet and rarely shows any emotion other than annoyance or boredom. He tends not to speak anything which not needed. This trait is shared with his father, Taizou. It has been noted on numerous occasions that Hayato's bad habit of hitting people on the head comes from Shizuka. He is not prone to angry outbursts but uses baseball batting as an outlet to vent his emotions.
He cares for his family and friends deeply, threatening to send Inui "flying to the sky" if he hurts "Ryuuko-san" (Ryuuichi in disguise as a girl) and also searching for Taka who runs away after his mother refuses to buy him a carp jet. He loves baseball—his biggest wish is to play at Koshien Stadium—and he is good enough to be considered the club's ace (though he himself describes the club as being "weak" repeatedly).
Hayato is the first born son of middle school science teacher Kamitani Shizuka and high school chemistry teacher Hebihara Taizou. As a child, Hayato had a somewhat abnormal relationship with his father Taizou as he was a very strict parent who profusely checked his son's teeth for cavities, never spoiled him and demanded Hayato never refer to him as his father in school. However, before his younger brother Taka was born, Taizou and Shizuka divorced and Taizou left the family, making Hayato harbor hatred for his father for not raising Taka and also not being able to properly tell him that he is his biological father. However, Hayato adopts his father's discipline and advice at times to control Taka's misbehaving.
He considers his younger brother Taka as being loud, brattish, and obnoxious, often annoying him behind his limitations. Even so, he loves his brother dearly, but is distant in showing it. Hayato's kinder feelings for Taka are shown on rare occasions when he is patient with Taka. Hebihara notes that Hayato rarely cried as a child in contrast to Taka, who cries often when upset.
He often resorts to violence such as hitting his younger brother on the head when he deems him to be annoying or when his brother is misbehaving. Sometimes this is extended to the other children (even Kirin to the disbelief of Ryuuichi) and his acquaintances. This is similar to his mother, even though she ironically scolded Hayato not to do so even with her similar tendency.
He shows a considerate and helpful side when it comes to Ryuuichi and Kotarou, especially when they face an occasional problem. At other times, he appear to be protective of both of them. He is popular with the girls at school who are attracted to his cold personality. On Valentine's Day, he receives plenty of love letters and confessions, though he rejects them all, seeing them as a nuisance.
- Hayato is repeatedly forced to disguise himself as a girl, and referred to as "Hayako" by Usaida to trick Satoru, and later, alongside Ryuuichi, pretended to be miko (shrine maidens). On both occasions, the boys are made to pretend to be girls by Yayoi.
- His habit of hitting people who annoy him is something he picked up from his mother, revealed when she hits him and then a sleeping Usaida.
- He is good at the sciences but really bad at the liberal arts. And he is described as being able to do well (in exams) when he tries hard.
- He doesn't have a sweet tooth, but he'll make an exception for tamagoyaki (sweet egg omelette).
- "Haya" from Hayato refers to "hayabusa", meaning "peregrine falcon".
- Ryuuichi points this out, as Usaida notes how even as birds, Hayato and Taka are siblings (as "Taka" means "hawk").
- He is voiced by Umehara Yuuichirou in the anime.