Kiyoshi Ōmizu (Japanese:
Ōmizu has thick eyebrows and sharp eyes, resulting in a keen and enthusiastic look. He wears his dark hair slicked back but with a leftover strand of hair on his forehead.
Ōmizu is incredibly hot-blooded. He is always pumped up and even instructs his players in the same fervent manner. It is said that he has a preference toward players who exhibit the same enthusiasm, implying that he finds it harder to deal with more laid-back ones like Kuguri.  However, he is always encouraging of every one of his players. Oomizu is seen trying to get Kuguri fired up just before Nohebi's match against Nekoma .
Not much is known about his background, but he appears to have been the coach for Nohebi Academy's boys' volleyball club for a while now due to his familiarity with the team's play style.
Spring High Preliminary ArcEdit
Ōmizu and his team faces off against Nekoma High for the last remaining spot in the Tokyo Representatives Selection Playoffs in hopes of advancing to the Spring Interhigh. Prior to the match, he approaches Kuguri to entrust him the starter positon in place of their ace after Numai dislocated his right thumb in the previous match. He tries to get the laid-back Kuguri to become fired up with some hot-blooded encouragement to no avail. 
As a coach, he is very encouraging toward his players. He is well-aware and encourages the team's style of riling up the enemy and gaining the referees' favor. Nevertheless, he still stresses the importance of improving the players' individual skills. He often holds meetings with his players to discuss what he needs to be improve on. After the loss to Nekoma, he is seen graciously accepting his team's loss before informing his players of an upcoming meeting after they go back.
Ōmizu has a good relationship with his players. He is supportive of the team's unconventional style of play while also emphasizing on individual improvements in skills. In turn, the team respects him. Some players, like Numai, are familiar with Ōmizu's hot-blooded personality and his preference toward players who acts similarly.
- Current concern: His ten-year-old daughter looked at him like he was nuts when she caught him bawling his eyes out over a Dis*ney movie.
- Kiyoshi (清心) - Clean/Pure Heart
- Ōmizu (大水) - Big Water; Flood
- "You lot have a knack for riling up the opposing side...and pulling the wool over the referee's eyes. That's been your strategy for as long as I can remember..but that's not good enough! You can do better!" (To Nohebi's volleyball club, Chapter 206)