Kazuhiko Hanawa, commonly addressed as Hanawa-kun, is a third-grade elementary school student and a classmate of the title character. He stands out immediately due to his distinctive appearance, which reflects his privileged upbringing. He is known for his brown, side-swept hair that is typically flicked to the left. In contrast to his peers, his daily wardrobe is notably formal and elaborate, usually consisting of a cream or white long-sleeved shirt with a white collar, an indigo waistcoat, an orange-red tie, black shorts, white socks, and black shoes. During the summer, he wears a sailor-style uniform. On more formal occasions, he might be seen in a white suit.

Hanawa comes from an extremely wealthy family; he lives in a large villa and is often cared for by a butler, as his parents are frequently overseas on business. This background heavily influences his personality and mannerisms. He carries a posh and elegant air, often speaking in a refined manner and referring to his classmates, particularly the girls, as baby. While he generally tries to focus on the positive aspects of any situation, his privileged life sometimes leads to behavior that can be perceived as slightly snobbish or vain, especially when he is showing off possessions that his friends, like the Sakura family, cannot afford. He is deeply concerned with maintaining his polished image and shows visible shock or dismay when caught in an embarrassing or undignified situation, such as having illegible handwriting or stepping on something unpleasant in the aftermath of a flood.

Despite his wealth, Hanawa is fundamentally a kind, generous, and helpful child. He does not hesitate to share his fortune with his classmates, regularly bringing back souvenirs for everyone from his trips abroad, such as miniature Eiffel Towers from Paris, and hosting lavish parties at his home for events like Christmas and Halloween. His generosity is frequently extended to Maruko, whom he often helps in practical ways. For instance, when Maruko was struggling to learn how to ride a bicycle, he lent her his own four-wheeled bike to practice with. He has also been known to fulfill the wishes of others, such as arranging for a photographer to take a family picture for the Sakuras or teaching a friend of Maruko's grandfather how to dine at a French restaurant.

His relationship with Maruko is a significant aspect of his role in the story. While Maruko initially found him odd and pretentious, Hanawa seems genuinely fond of her and often goes out of his way to make an impression on her. He has been shown trying to look impressive in front of her, complimenting her when she wears a hairband, and even teasing her gently. On her ninth birthday, he gave her a bouquet of nine roses and promised to give her a bouquet with an increasing number of roses for each birthday to come. This dynamic, where he shows a particular kindness and attention toward Maruko that differs from how he treats others, is a recurring and charming element of the series.

Hanawa's life of privilege has afforded him numerous hobbies and talents not available to his peers. He is well-traveled and enjoys sharing stories about his overseas trips and knowledge of other cultures. He takes weekly lessons in English and French, and his English is fluent enough to help a lost foreign visitor find a bus station. His education also includes piano, violin, and even Indian philosophy. His favorite sport is tennis, and he is also skilled at playing cards. Among his most prized possessions are a Swiss clock and the letters he receives from his parents abroad. He is also noted to be a huge fan of actress Audrey Hepburn and proudly owns her autograph. Through all these traits, Hanawa serves as a source of wonder and often comic relief, representing a drastically different world from that of his friends, while his fundamental decency makes him a beloved and trusted member of the class.