Diamond no Ace Wiki
Kataoka Tesshin
Seidou High School
Baseball Coach
Bats: right Throws: right
Kanji 片岡 鉄心
Nickname Coach Shades (クラサン Kurasan) [1][2]

Boss [1]
Big Boss [1]
General (将軍 Shōgun) [1][3]
Demon Child (悪童 Akudō) [4]
Soul Ace (魂のエース Tamashī no Ēsu) [5]
Tetsu [6]

Gender Male
Date of birth 25 December
Place of birth Tokyo
Bloodtype O
Height 184 cm (6' 0.5")
Weight 77 kg (169 lbs)
First Appearance
Manga Act I - Chapter 4
Anime S1 - Episode 3
Voice Actor Hiroki Touchi
I don't know any other coach who knows his players this well while keeping a distance.
Takashima about Kataoka[7]

Kataoka Tesshin is the coach of the Seidou High School Baseball Team. He is an alumnus of the school and has played as a pitcher in the past.[8] He is also a Modern Japanese teacher.


Kataoka is known as a strict coach, but he also praises his players and says reassuring things to them from time to time. Every thing he does is for the benefit of the team. He spares no effort. If he wants his players to make a significant step forward, he himself takes part in training.


Kataoka was a rowdy unmanageable brat with an evil look in his eyes and no manners. But he had the strongest will not to lose and is the one who ran the most among all the generations of Sakaki Eijirou's disciples. Sakaki was charmed by Kataoka's burning fighting spirit and gave him the ace number in the fall of his 1st year. At this time Kataoka was still not skilled enough, so there were objections from the higher-ups. Kataoka tried to listen and take advice, changing himself, and, whether due to unbelievable fighting spirit or self-awareness as the ace, he suddenly made a leap in his development as a pitcher. In the Fall Tournament they reached the semifinals. But in the summer of Kataoka's 2nd year they won the West Tokyo Regional Tournament and made it to Summer Koshien, Shutting down one strong team after another as they went, Katoka led Seidou to the Koshien Final, and they finished as the runners-up (Kataoka was said to have the unbreakable heart of steel, 'heart of steel' being what his name, Tesshin, literally means).

The qualified for Spring Koshien at the end of Kataoka's 2nd year as well and reached the quarterfinals. In Kataoka's 3rd summer they narrowly lost the chance to go to Koshien again, but he was the ace until the end. Kataoka felt guilty for not being able to make Seidou and Sakaki No.1 in Japan. He clearly said to the coach that he wanted to repay the favor to the high school baseball that had changed him and return to Seidou as an instructor which would have been difficult had he chosen to go pro. When Kataoka graduated from university, Sakaki resigned because he believed he could leave Seidou in Kataoka's capable hands.[9]

Relationships with other characters

Sawamura Eijun

Kid, your feelings are that of a magnificent Ace!
— Kataoka to Sawamura [10]

Kataoka praises all his players and says reassuring things to them if he sees it fit. But he doesn't show it quite like how he does it with Sawamura: feeling Kataoka’s reassuring hand on his shoulder is Eijun’s privilege, and it speaks volumes of where Kataoka’s affections and his faith rests (this may partly be due to seeing a bit of himself in Sawamura). Kataoka never once lost faith in the young pitcher when the latter suffered from the yips, which is evidenced by the fact that he didn't pull him off the team.

Sawamura is also always nervous about Kataoka potentially bringing up his infamous reputation for sleeping in class. Since his 2nd year in high school, Sawamura and co have started taking Kataoka's class, and Sawamura has to remind himself to not fall asleep, fearing the consequences he may have to later face in practice.[11]

Miyuki Kazuya

Kataoka acknowledges Miyuki's skill as catcher and trusts him greatly during games.

Ochiai Hiromitsu

Ochiai is curious about Kataoka and wants to know how good the later can be at being a coach. He often confronts Kataoka about their different way of coaching. Although they disagree from time to time Kataoka values Ochiai’s opinion as a coach and respects him.

Sakaki Eijirou

Sakaki was his former mentor and Seidou's former coach, now he is working as the head coach of the Hosei University baseball club. Sakaki has stated that he is returning to high school baseball and will be the new head coach of Yura Technical High School in West Tokyo.


  • He is also an alumni of Meiji University, which is also called Meidai or M University. [12]
  • Kataoka is a smoker, but this fact was censored in the anime.[13][14]


  • "I dare say that there was no one who taught him such daring pitching form. His flexible joints allow to pitch so that the ball's movement and only be seen at the last seconds. When comparing natural talent...he may outdo the other two." - about the 1st-Years [13]
  • "Why didn't you all take the field with that kind of spirit from the beginning? After High School Baseball there is nothing else for you." - to the 1st-Years [15]
  • "Even after being hit, he still has bright eyes. He is like a kid, who has just learned baseball." - about Sawamura [16]
  • "Every throw, every step and every swing are a reflection of your true selves. No need to waver! Believe in your own style!" - to the team [17]
  • “I’m not looking at a first year like you for perfect contents yet. Make it count towards the next time - this experience." - to Sawamura [18]
  • "A giant will fall if you break his legs" [19]
  • "I don't know any other coaches who knows the players this well while keeping a distance." - Takashima [7]
  • "These kids have it in them right from the start. The strong will to face their opponents." - about the team [20]
  • "I don't plan on sacrificing the entire team just for Furuya." - to Ochiai [21]
  • "Even if we've come this far in the tournament, in sports there is no way to know what might happen. You might be asked to go and play at any moment. Are you prepared for that mentally? Because I'm going to treat this game as any other official match and give you signs with that in mind. Let's take them down!" - to the "reserve team" [22]
  • "The enemy is within oneself. Fighting full out with all of your power in the real game is the shortest path to victory."
  • "Ah, right! Boss, you, too, prepare yourself please. Only 2 wins left till Koshien! And we won't let you just resign and abandon the team that won the right to be there!" - Sawamura [23]
  • "There is no shortcut to glory. A player who cannot distinguishes between assertiveness and arrogance play is not needed by the team." - to Furuya[24]
  • "Overconfidence leads to hubris, while too much humility results in servility. So from now, I want you to keep walking like you did until now, keeping your feet firmly planted on the ground. I'm looking forward to your next performance." - to Sawamura



  1. 1.0 1.1 1.2 1.3 Established by Sawamura
  2. Act I - Chapter 9
  3. Act I - Chapter 72
  4. Act I - Chapter 323
  5. Act I - Chapter 412
  6. S1 - Episode 29
  7. 7.0 7.1 Act I - Chapter 204
  8. Act I - Chapter 342
  9. Act I - Chapter 324
  10. Act I - Chapter 9
  11. Act II - Chapter 59
  12. In Japan, popular universities often have their name shorten such as Tokyo University is called Todai while Meiji University is called Meidai
  13. 13.0 13.1 Act I - Chapter 17
  14. Act I - Chapter 148
  15. Act I - Chapter 14
  16. Act I - Chapter 16
  17. Act I - Chapter 97
  18. Act I - Chapter 110
  19. Act I - Chapter 124
  20. Act I - Chapter 206
  21. Act I - Chapter 223
  22. Act I - Chapter 319
  23. Act I - Chapter 317
  24. Act II - Chapter 71