Kazuki Kawai (河合 和己 Kawai Kazuki) is the captain and catcher of Tosei High School's baseball team.
During his first year, he had to watch his team lost in the first round and their loss wasn’t even due to being a bad team or facing a strong opponent, hence why he never underestimates the opponent even when it consists of only first years like Nishiura. He grew up into a good leader in his third year, as noted by Nishiura’s coach Momoe who calls him the heart and center of the team.
Kawai has black, spiky hair and dimples on his cheek.
Responsible and mature, he earns the respect of his entire team with a lot of his juniors also looking up to him. He is also a good leader and can tell when his teammates are troubled and often finds ways to lift their spirits. He can also be strict with them, as shown when he reprimands the team for underestimating Nishiura. However, he himself finds it hard to see Nishiura as a strong opponent after seeing the team in person, though he keeps this thought to himself in order not to demoralise the other players.
He also possesses good sportsmanship and genuinely advises Bijoudaisayama's catcher to play honestly in his subsequent matches after Nishiura, suspecting that he might be receiving signs from the spectators' stand which is illegal.
Kawai is an excellent catcher with a good throwing arm, and even Momoe couldn’t stop herself from admiring his throwing skill despite being on the opponent's side
Takase completely looks up to Kawai and is never short of praises for him. It reaches a point where Nakazawa gets annoyed with them and asks them to stop with their “married-couple” antics. Takase takes Kawai’s words not to underestimate Nishiura seriously, unfortunately to the detriment of the team in the beginning of the match as he becomes too nervous to pitch properly. Kawai is familiar enough with Takase's delicate personality to know the right timing to snap him out of his nervousness without bruising his ego. After they lost their first match to Nishiura, Kawai completely breaks down in tears after seeing Takase cries over his last match together with him, as the Summer Tournament would be the third years’ final chance to play baseball.
Kawai is close to Rio as they have been friends since middle school along with Takase. However unlike Takase, Rio is a lot more carefree when speaking with Kawai. He often snaps at Kawai when the latter annoys him despite their two-years age gap, much to Kawai's amusement. He also knows Rio's older brother Roka, whom he considers as his rival. Rio can be seen tearing up for Kawai after their loss against Nishiura, realising that it is Kawai's last match as a high school baseball player.
Roka was the third year senior whom he witnessed losing in their first game during Kawai’s freshman year, and they remain in contact even after Roka had graduated. He appears to have a friendly rivalry with Roka. They are close enough for Roka to treat him to a meal and dig out Nishiura's secrets from him before their match against Bijoudaisayama, the team that Roka currently coaches. He also joins Roka to watch his team's match against Nishiura. However, Kawai also doesn't hold Roka in much high esteem and believes that playing dirty is not above him. Though he cannot confirm his suspicion during the game, he still goes to great lengths to separate the team's catcher Takeshi from Roka after their match against Nishiura and advises him to start playing honestly in their subsequent matches.
Kawai seems to have an easy-going relationship with Shimazaki. While he is strict with the rest of the team when they underestimate Nishiura, he only lightly chides Shimazaki for repeating the same sentiment when it is just between the two of them. Together with Shingo, they try to figure out the trick behind Mihashi’s weird fastballs during their match against Nishiura.
- He seems rather smitten with Momoe and struggles to steal glances at her when she is giving signs to her team.
- He has the best grades among the baseball team (though this may not say much as Roka claims their baseball team is mostly made out of idiots), and takes his studies seriously in order to have more options for colleges eventhough he can be admitted by sports recommendation alone.