Kazuomi Ōga (大神 和臣 Ōga Kazuomi) is a third-year student at Aoba High School, and a close classmate of Arata Kaizaki after he became a teenager. He is very smart and always gets the highest score among the boys in his grade, which is why he is recurringly selected as the class representative. This, along with his appearance, contrasts with his poor athletic ability and denseness when it comes to romance.
Kazuomi has light brown hair and brown eyes. While attending Aoba High School, he wears his elder brother's uniform (white shirt, black tie, dark gray full trousers and a light gray full sleeve sweater), which happens to be too loose on him. He has matching piercings with Kariu in his left ear,which was done by his brother. He has received compliments from both, An and Kaizaki on having an attractive physique. Arata has also called Kazuomi good looking multiple times.
He is very focused on school, and spends most of his time perfecting his grade to get into college. He's seen as being dense in the matters concerning love and relations as he did not know about Kariu's feelings for him.He cares for his friends very much, and often looks up to Kaizaki for advice. He also feels embarrassed after mentioning that he has a girlfriend as a way of boasting to Kaizaki.
He has said that his family doesn't have a large amount of money, which is partially why he works so hard to be top of his class. This way his family doesn't have to pay for his meals. He seems to love his brother very much, getting one ear pierced by him.
Arata Kaizaki - Ohga shares a warm relationship with Arata. He constantly helps Arata with the retry tests he has to take,even though he is irritated with the lack of progress. It is due to Kaizaki that Ohga realises his feelings for Kariu.
Rena Kariu - Ohga has been close friends with Rena since their middle school. As he has a dense personality, he did not realise that Kariu loved him. Kaizaki makes him realise his feelings for her and he confesses to her during the Summer Festival, the two of them becoming a couple after mutual confession from Rena.
- Spellings of his name include:
- In Japan, the English spelling of his name is "Kazuomi Ohga".
- In licensed English translations, his name is spelled "Kazuomi Oga".
- Under the Modified Hepburn system, the romanization of his Japanese name would be "Kazuomi Ōga".
- Under the Japanese Government Ministry of Foreign Affairs Hepburn Variant used for passports, his name would be romanized as "Kazuomi Oga" (although the ministry also allows other spellings per consultation, such as "Kazuomi Ohga" or "Kazuomi Ooga")
- He pretty much always eats udon for lunch. 
- In Report 22 he used a smartphone with a orange-blond shell that matches the color of his hair. However in Report 45 and later the color of his phone changed to a brighter yellow color.
- Ōga's surename is an homage to the Ōga Station in Ōita, Japan.