Hideo Harada, most often referred to as Dr. Harada or Harada-sensei, is a character in Chihayafuru who serves as a mentor and the head of the Shiranami Karuta Society. Beyond his role in the karuta world, he is a practicing medical doctor, balancing his professional career with his deep passion for competitive karuta. His background is marked by a significant sacrifice; as a young man, he was a talented player who once challenged for the Meijin title at age twenty-six. However, his career as a doctor took precedence. His medical placements sent him to regions like Okinawa and Hokkaido where competitive karuta was nearly nonexistent, causing him to step away from the game during his prime years. It was only after establishing his own private practice in Tokyo at the age of thirty-seven that he could fully re-immerse himself in karuta, by which time his natural physical gifts had already begun to wane.

In terms of personality, Dr. Harada is a kind and encouraging figure who possesses a profound and insightful understanding of karuta. He is fiercely competitive, not only for himself but also as a passionate supporter of his students and a proud representative of his karuta society. This competitive fire is paired with a tendency for dramatic and exaggerated expressions, such as his famously effusive welcome of young Chihaya, Arata, and Taichi to his society. He is known for teaching an aggressive, offensive style of karuta aimed at taking cards directly from the opponent's side, a philosophy that deeply influences his protégés. His primary motivation throughout the story is his enduring, almost stubborn dream to become the Meijin, a title he has chased for decades despite his advancing age and declining physical condition. This pursuit is not just about personal glory but also about proving that experience and strategy can overcome the raw speed of youth.

His role in the story is that of a foundational mentor and a symbolic figure of perseverance. He is the head of the Shiranami Society, where protagonists Chihaya Ayase and Taichi Mashima train, and he previously taught Arata Wataya when they were children. Dr. Harada is the one who recognized and nurtured Chihaya's raw, natural talent for karuta early on, becoming her staunchest supporter and advisor. He plays a direct and pivotal role in the competitive narrative, most notably when he faces his former student Arata in the Meijin challenger finals, a match that represents a clash between his seasoned, hard-won experience and Arata's youthful, inherited brilliance.

Dr. Harada has several key relationships that define his character. With Chihaya Ayase, he is a beloved coach and father figure; her internal monologue during matches often returns to his advice, and she has deep loyalty to him. With Taichi Mashima, he is a mentor who affectionately nicknames him Eyelashes-kun and engages in a more nuanced, strategic student-teacher dynamic. His relationship with Arata Wataya is complex, blending pride in his former student with a fierce rivalry, as seen when they compete directly for a chance at the Meijin title. He also has longstanding rivalries with other figures in the karuta world, such as Akio Kitano of the Suihoku Society, a rivalry rooted in their youth, and Midori Makino, a professional reader who holds a grudge against him for something he did in the past. In contrast, his relationship with Isami Kuriyama is more friendly, a rivalry born of mutual respect.

Dr. Harada undergoes significant development, primarily centered on his struggle against the physical limitations of age. The story explores his journey of adapting from a player who relied on superior hearing and speed—gifts similar to Chihaya's—to a veteran who must use tactical intelligence and psychological pressure to win. His character arc culminates in his realization that he must abandon his youthful playing style to embrace his identity as a cunning, experienced competitor, learning to win through strategy and composure when his body can no longer keep up with younger players.

His notable abilities in karuta are a direct adaptation to his physical decline. He employs a highly aggressive offensive style. One of his most distinctive talents is the ability to detect the Joker card, which is the card in a match that is unlikely to be read, allowing him to manipulate the flow of the game. He also developed a technique called Sudden Stop Acceleration specifically to counter the current Meijin, which involves aggressively swinging his hand but stopping abruptly to avoid committing a fault. In his youth, he possessed superior hearing, akin to Chihaya's, a talent he has since lost but compensated for with his strategic mind. His overall style and tenacity have earned him nicknames from other players, including Intelligent Bear.