|Manga Debut||Chapter 19|
|Anime Debut||Episode 10|
Hiroshi Tsuboguchi (坪口 広史 Tsuboguchi Hiroshi) is karuta Class A player, and the ace player of Shiranami Karuta Society, and the Homei High School Karuta Club. He'll be playing in the Master tournament this year.
A good karuta player. He does not like to play against high school players because they are still developing physically.
Despite being a Class-A karuta player and the Ace of Shiranami Karuta Society, he is also quite lazy. Harada always mentioned about his lazy behavior.
Tsuboguchi's junior in Shiranami Karuta Society, along with Chihaya and Arata. Tsuboguchi also admired Taichi and acknowledged his hard work. After Homei High and Mizusawa High played their first karuta match, Tsugobuchi told them that he admired how much effort Taichi poured into karuta. In the semi-final of Yoshino Society Tournament, Tsuboguchi told Taichi that he made it that far because of his own skill, not because of luck. In the semi-final for East Meijin Qualifier match, Tsuboguchi fought against Sudo and mentioned that Taichi did a very good job beating Sudo, showing how good Sudo is and how much better Taichi had become.
Tsuboguchi's junior in Shiranami Karuta Society. When pitted against her in the semi-final of Yoshino Society Tournament, he forfeited.
- Tsuboguchi is a Karuta teacher adviser.