The male protagonist, Oriyama Karin 's husband.
Nao is said to be very handsome. He is well loved by all the girls at school (including Karin ). He has dark brown hair and teal coloured eyes (as seen on coloured pages of the manga). He seems to be quite tall and Karin notes that he has a broad back.
Nao seems to be a quite level headed and responsible young man. Although he is initially cold and indifferent towards Karin, he warms up to her quite quickly due to her pure and optimistic attitude. Nao seems to have no problems with puuting on an act, as shown when he spoke to her before the wedding and at school. He wished to get out of his parents' house by any means due to their arguing. Since his mother says that Nao is the only reason that she married his father, Nao shows a strong dislike for women who fall in love with men based solely on their looks, saying "I despise them". Nao also seems to have a strong sense of pride and responsibility, refusing the ask Karin's father for more money after she blows it all and then refusing to accept the money and telling Karin's father that he would pay it back with interest. Nao is very bright and is one of the top three students in the school. He also frequently plays soccer.
Nao's first appearance is in Karin 's memory, and then again in a photo. His first real appearance in the manga is when Karin goes to watch him play soccer at school and talks about how they will be married soon. At the beginning of the manga, he seems very kind and patient with Karin and her father menttions to Karin that Nao looked very excited to be marrying her as well. At the wedding he is able to patiently pacify Karin 's tantrum and the two get married.
However,once they get into their apartment Nao immediately begins moving furniture to create two rooms. He thanks Karin for marrying him and tells her that he only agreed to the marriage as it meant that he could move out of his house and be away from his parents, but when he realises that she actually likes him he tells her that he dislikes her the most (as she liked at first him because of his handsome looks).
He sets up some rules for Karin which basically say that they have nothing to do with each other and are just living in the same house. Ouch. After this he goes straight to sleep in his room, leaving poor Karin all alone to deal with what he revealed to her. The next morning when Karin wakes up he has already left, leading Karin to realise that he was serious.
Karin stays after school and watches him play soccer but when she asks Nao to walk home together he rejects her like he does with all the other girls. This is not because he is trying to be cruel to her, but actually that he doesn't realise that she doesn't know the way home. When Karin comes home, he is waiting for her and scolds her for leaving the house in a messy state. When she starts to cry and tells him what she went through he pities her and teaches her how to turn on the hot water and also buys her dinner. When he goes out to buy food Karin sees him and opens the bathroom window, after they finish speaking Nao revelas to her that she has been 'on display' the whole time. After she closes the window, halfway down the stairs, Nao has stopped walking and is blushing.
The next day they are going to school together (with Karin 5 metres behind) when their next door neighbour reveals to Karin that Nao accidentally confronted her multiple times thinking she was Karin returning home.