Hiroshi Tsuboguchi

Tsuboguchi is experienced and capable but has a notably relaxed side. Harada criticizes him for laziness despite his position as Shiranami's ace, creating an amusing contrast between his high competitive level and the amount of effort his teacher sometimes believes he should be showing.

He is considerate toward younger players. Tsuboguchi understands that high-school competitors are still developing physically and is reluctant to treat matches against them as though age and experience create no difference.

He also recognizes effort in players whose progress is less spectacular than that of obvious prodigies. His encouragement of Taichi is particularly important because he sees how much work lies behind Taichi's advancement.

Tsuboguchi is an established Class A player and one of Shiranami's strongest active competitors. His rank allows him to participate in the same advanced tournaments as title contenders and other veteran society players.

His experience gives him a broad technical foundation rather than one heavily emphasized specialty. He understands positioning, memorization and match management well enough to compete deep into major tournaments and to teach those skills to high-school students.

As an advisor to Homei High School's club, he can also analyze team karuta from a coaching perspective. This requires attention not only to his own board but to lineup construction, player development and the differences between individual and school competition.

Tsuboguchi is introduced through the Shiranami Society, establishing that Harada trains accomplished adult players as well as Chihaya and her childhood friends. He remains one of the society's strongest representatives as Chihaya and Taichi move into higher competitive classes.

His work with Homei High School later brings him into the high-school tournament environment from another direction. He is both an opponent within adult Class A competition and a teacher responsible for developing younger players.

Tsuboguchi also becomes significant to Taichi's development. He explicitly recognizes the work Taichi has invested in reaching stronger competition and rejects the idea that every good result can simply be dismissed as luck.

Hideo Harada is Tsuboguchi's longtime teacher and the head of the Shiranami Society. Hideo Harada regards Hiroshi Tsuboguchi as one of his strongest players even while complaining about his tendency toward laziness.

Taichi Mashima is Tsuboguchi's junior at Shiranami. Hiroshi Tsuboguchi recognizes Taichi Mashima's persistence and makes a point of crediting his tournament progress to skill and effort rather than luck.

Chihaya Ayase is another Shiranami junior. Hiroshi Tsuboguchi follows Chihaya Ayase's rapid development from an enthusiastic young player into a serious Class A competitor.