Yamiji appears to be of middle age with short grey hair that he keeps spiked upwards. He has thick dark grey eyebrows and is usually seen wearing square framed glasses. Yamiji seems of average height with a muscular build.
As the head coach, Yamiji takes things seriously most of the time but he is also understanding and encouraging toward the players. He is also shown to have a silly side that is mostly seen when he and Bokuto chest bump when the ace makes a successful play. Despite this, he also tends to be annoyed when Bokuto falls into one of his mood swings.
Yamiji appears to have been the coach for Fukurōdani Academy for several years and has helped lead the team to Nationals numerous times.
Spring High Preliminary Arc
Fukurōdani vs Nekoma
Fukurōdani plays against Nekoma to determine the city representative for the Spring Tournament. Fukurōdani is able to stay strong for the first set but starts to face trouble in the second set when Nekoma devices a plan to contain Bokuto. He tries to keep the team in high spirits by reminding them that not even Nekoma would be able to withstand their attacks when Fukurōdani is playing in top form.
When Bokuto finally falls into one of his moods when he forgets how to hit cross shots, Yamiji calls for a time-out so they can figure out why he has suddenly become thrown off his game. Fortunately, Akaashi was able to quickly figure out a way to get Bokuto back to top form that would eventually lead to Fukurōdani winning the match and moving to the finals.
Tokyo Nationals Arc
Fukurōdani vs Eiwa
In Fukurōdani's first match of the tournament, Bokuto becomes depressed much earlier than he normally does which causes the team to fall behind in the score against Eiwa High School. During a time-out, Bokuto admits that he's upset that they are not playing in the main arena and is quickly scolded by Yamiji for getting so emotional despite the fact that they had talked about this just the day before.
Even with Bokuto still upset, Yamiji is proud that Fukurōdani is able to stay strong and eventually catch up. Fukurōdani went on to win the match and advance to the second round.
Fukurōdani vs Mujinazaka
Knowing that many people present will have their eyes on Bokuto and Wakatsu Kiryū, Yamiji encourages the rest of the team not to be outdone by their ace. Despite his encouraging words, Fukurōdani starts off shakily and it becomes clear that Akaashi is struggling during the first set. Yamiji decides to have the second-year setter brought out in order to let him calm down; although he would soon be caught off guard when Akaashi expressed frustration at how he was behaving.
Yamiji decides to question Akaashi on what he thinks of the meaning on their team banner 'Pour all you soul into each ball'. At hearing Akaashi think the banner is pretty clear and means exactly what it says, Yamiji explains that the motto really means more of securing the next step; similar to securing the next point of a game. At hearing Akaashi speaking to himself, Yamiji does not understand what the setter is talking about. Fukurōdani lost the first set but now that Akaashi is back on track, Yamiji sends him back into the game. As the match continues, Fukurōdani is able to catch up and Yamiji is at one point seen chest bumping with Bokuto in celebration of a play.
As the coach, Yamiji gets along with his team well. Like the rest of his team, he is aware of Bokuto's emo mode, and knows when to call time-outs during games.
Yamiji appears to have a close relationship with Bokuto. Since Bokuto's first year at Fukurōdani, the two are shown to do chest bumps during good plays. Yamiji is also aware of and annoyed by Bokuto's mood swings and has tried to talk with the ace about this problem several times.