As class representative of 2-C, Hanai takes his duties seriously, always trying to keep his classmates (especially the males) in line. Unable to have second thoughts, he always says exactly what comes into his mind regardless of the consequences. Although he is against perversion, he occasionally cannot help himself from temptations such as viewing sexy photos of Itoko Osakabe under the excuse of validating their authenticity or "consficating" Ganji Nishimoto's entire porn tape collection.
As a child, he was shy, weak, and always been bullied by other children. That changed with a little help from his childhood friend Mikoto Suō.
Hanai (in the original Japanese dub) sometimes speaks with a (somewhat-literary) touch, such as his uses of -tamae instead of kudasai and less colloquial vocabs that one would normally use in an essay than in speech.
Recently, Hanai was floating around in the air on the kite. Although he briefly made landfall in South America and later on a cruise ship on which his classmates were on, he drifted back to Japan from the south, but was propelled far away once again by a bag thrown by Lala at the end of Second Term.
Harima refers to Hanai with the nickname "Megane (眼鏡)" ("Eyeglasses").
Hanai is shown to be very handsome when he removes his glasses.
According to the last Japanese poll performed by the publishers of the manga, Hanai is currently the fifteenth most popular character in the series.
Hanai attends the same dojo as Mikoto and has a black belt in kenpo as well, as such he is shown to be on par with Harima in hand-to-hand combat. He is one of the best athletes in Class 2-C, going through some arduous training to prepare for the sports festival. Hanai's long tenure on a kite for two weeks without any food before making landfall also shows that he has a great deal of endurance, and how long it took him to drift back to Japan from the south is unspecified. He is also a decent cook.
Hanai is hopelessly in love with Yakumo Tsukamoto, so strongly that she can read his mind literally from a mile away. He tries very hard to join the Tea Club that Yakumo is in, but is banned by his classmate Akira Takano, the club president. Yakumo has not explicitly rejected him, but Hanai persists even though it is obvious that she lacks interest in him.
Hanai is also Kenji Harima's main rival in school, usually due to misunderstandings between them which tend to be sorted out through violence. The main cause of their rivalry was Hanai's misinterpretation of the Harima/Yakumo relationship, although this aspect of their rivalry later cools when Hanai discovers that Harima is not in love with Yakumo. Although they put all of their strength into their matches, they always get interrupted in the middle, or end in a draw.
Despite Hanai and Mikoto having their own love interests, characters around them sometimes think that they are too close to be just friends, especially when Hanai called Mikoto "Miko-chan" during the Survival Game when she was shot by Harima in the beginning of the second season. Although Hanai is mainly in love with Yakumo, he does on very rare occasions show feelings towards Mikoto, as seen during her birthday in the first season of the series when Yakumo could not read his mind for a moment . In the manga, when all the students were told of their futures, Hanai sees himself as being married to Mikoto and having four children, a vision Mikoto also coincidentally has. This confuses him due to his feelings for Yakumo.
Recent chapters suggest (and possibly confirm) Hanai's repressed feelings for Mikoto. A brief bout of amnesia brought on by an injury sustained while protecting Mikoto leads Hanai to conclude that he and Mikoto were a couple, after he witnesses her concern for his well-being. This prompts Tenma, Akira and Eri to hold a mock wedding with the intention to "shock" Hanai's memory back. He does regain his memory when he sees Yakumo on his way to the altar. As he and Mikoto are about to kiss, he reveals that he has regained his memories. Recognizing that Mikoto was willing to take the charade to the end by refusing to turn away from the kiss, he implies that he would "meet her there" should the situation ever arise again.