Tadashi Yamaguchi (Japanese:
Yamaguchi is a young-looking boy with an average build. He has dark grayish green hair with a flyaway piece of hair sticking up at the top. Back in middle school, he was teased for his freckles and overall scrawniness. He seems to have grown into it now, and isn't bothered about it as much.
After joining the Karasuno volleyball team during games, Yamaguchi wears Karasuno's black, orange, and white uniform with the number 12 on the back. He also wears knee pads, and white volleyball shoes with black accents.
Outside of matches and practice, Yamaguchi wears a black gakuran, the Karasuno uniform.
Yamaguchi is a pretty shy person who relies on others. Though he is generally a nice person in the anime, he tends to snicker along or join in with Tsukishima whenever he's mocking others, especially Kageyama and Hinata, in the manga.
He is hardworking, as shown when he sought for extra training on his own and how he continued practicing outside of the team, after seeing how weak he was compared to his other teammates.
After a fatal loss in the match against Aobajohsai High, he gained a lot of confidence thanks to his teammates and Makoto Shimada, who has helped him practice the jump float serve. During the summer training camp, he even stood up against Kei Tsukishima, resulting in him being surprised at Yamaguchi's actions and even calling him "cool" for the first time. Tsukishima started working harder, and their relationship returned to normal after that event.
BackgroundBack in elementary school, Tadashi was teased for his freckles and overall scrawniness. Once Tsukishima saved him from some boys who bullied him by calling them pathetic. Despite thinking that he was included among the ones Tsukishima insulted, Yamaguchi still grew attached to him and looked up to him, he set his goal to become "as cool as him".
Karasuno High Team Formation Arc
Yamaguchi and Tsukishima join Karasuno Boys’ Volleyball Club a few days after it begins for the new school year. That evening, they visit Hinata and Kageyama at the field where they’re practicing. Tsukishima mocks the two while Yamaguchi stands off to the side, smirking along. When Hinata asks about Tsukishima’s height, Yamaguchi answers for him, irritating Tsukishima. On the way home after this, Yamaguchi asks Tsukishima if something's wrong and Tsukishima angrily replies that he hates hot-blooded people like the other two first years.
3-on-3 First Years Match
On the day of the match, Tsukishima begins by insulting Kageyama and Hinata and Yamaguchi hurriedly warns Tsukishima, only for the latter to retort that he’s using provocation on purpose. Yamaguchi doesn’t show much of his abilities during this match as Daichi covers the receives and Tsukishima covers the blocks. In the end, his team loses to Kageyama and Hinata's
At the end of the match, Yamaguchi calls out to Tsukishima worriedly as Hinata attacks him in an attempt for a handshake. Yamaguchi gets his team jacket and hesitantly poses with Tanaka and the other upperclassmen.
Aobajohsai Practice Match
He is seen with Kageyama, Tsukishima, and Tanaka intimidating two members of Aobajohsai. He does not play in the match. He is upset by the fact that he is the only first year not playing.
Karasuno vs Date Tech
Yamaguchi did not play in this match but he provided the playing members of the team with praise, cheers and encouraging words.
Karasuno vs Aobajohsai
During a timeout the players who were just on appear incredibly exhausted to Yamaguchi, but he claims to be jealous, and that he's sick of being the only first year who never gets to play. After being convinced by Sugawara and Ukai, Yamaguchi swaps with Hinata to attempt the jump float serve, with the intention of changing the match's momentum. However, he makes an error and the serve goes into the net. This upsets him incredibly as he leaves the court nearly in tears.
Later, he talks with Makoto Shimada, his unofficial volleyball guide, about the match, who advises him about his choices in volleyball and reveals to him about his own experiences with volleyball. This motivates Yamaguchi to try harder in volleyball next time.
Tokyo Expedition Arc
Throughout the Arc he is seen multiple times practicing his float serve, mostly with his teacher Makoto Shimada, or Nishinoya.
When Kageyama and Hinata have trouble studying he is the one to convince Tsukishima to help them and is later seen helping them as well. When Yachi is first introduced to the Karasuno Players Yamaguchi thinks of her as "cute". He then recommends Hinata to ask her for help studying since she is in a advanced class.
During the training in Tokyo Asahi comments that his serve has improved a lot.
After the regular training he asks Tsukishima to help him practice which he declines. He then asks if he is going to practice anything by himself to which Tsukishima declines as well. Yamaguchi, worried about Tsukishima's lack of motivation, asks Hinata what he would tell Tsukishima. Hinata answers that he wouldn't say anything since he can`t even tell if Tsukishima likes playing volleyball in the first place. Yamaguchi explains that he thinks Tsukishima doesn't hate volleyball, since he wouldn't have come to Karasuno otherwise.
In the next episode we are shown a series of Yamaguchi's flashbacks. In the first one we see him being bullied by 3 kids. Tsukishima passes by and upon noticing exclaims the phrase "lame". Although Yamaguchi isn't sure what exactly Tsukishima was referring to he still admires him for being able to say it. Later he meets Tsukishima at the Volleyball Gym. He tells him that he came to check out volleyball since it seems safer then other sports. Tsukishima, in return, tells him about his brother. In the last flashback Yamaguchi is present when Tsukishima finds out his brother had been lying to him about being the Ace of the Karasuno team.
After Tsukishima decides to blow off extra practice once more Yamaguchi confronts him. He tells him that he has always admired his height, intelligence and coolness, but that his lack of trying to improve makes him "lame". When Tsukishima asks him how one can still give his best even though the chances of ever becoming the very best are almost non-existent Yamaguchi, remembering his failure against Seijoh, angrily exclaims "What else do you need besides pride?". Tsuki, obviously impressed then calls him "actually cool" and heads off to talk with Bokuto. After this Yamaguchi asks Hinata if he sees Tsukishima as a rival, to which he answers "obviously". When Tsukishima gives is his all and forces Bokuto to use a faint in the match against Fukurōdani the next day Yamaguchi is seen on the sidelines smiling.
Spring High Preliminary Arc
Karasuno vs Ohgiminami
Yamaguchi did not play in this match.
Karasuno vs Kakugawa
Yamaguchi did not play in this match.
After the preliminaries Yamaguchi is seen practicing multiple times, finally managing to get a serve in that Nishinoya is unable to return.
Karasuno vs Wakutani South
Yamaguchi gets switched in. He is once again very nervous even though Tsukishima and Ennoshita try to cheer him up. This results in his serve toss being to low and the ball barely getting over the net. Although the serve still scores a point Yamaguchi becomes nervous and hits his next serve without jumping in order to get it over safely. Karasuno still scores the point and wins the set but Yamaguchi is visibly upset about backing down. Ukai, who is returning from helping an injured Daichi, angrily walks up to him, ready to give him a lecture, but Ennoshita steps in. He explains that Yamguchi already knows better then anyone else.
In the stands Makoto Shimada explains to Saeko that a jump serve offers much more speed and that Yamaguchi`s only option to fight on equal grounds with his teammates is to give it his all.
After the match Yamaguchi leaves the rest of the team for a couple minutes for an unknown reason.
Karasuno vs Aobajohsai
A nervous Yamaguchi tells Yachi about his failure during the last match against Seijoh, which makes Yachi nervous. This takes Yamaguchi's worry off the match by focusing on Yachi.
During a 23:19 lead by Seijoh in the second set Yamaguchi silently urges Ukai to switch him in. We then see a flashback to after the Wakutani match. Yamaguchi went to Ukai to apologize for backing down during his serve, even though Ukai had already expressed his opinion on this during the Fukurōdani training match (Asahi did not do a jump serve in order to play it safe). He asks him to give him another chance.
Back to the Seijoh match, Yamaguchi is switched in and gets told by Hinata to score 10 points. On his note that that would end the match Hinata tells him that he would forgive him. As he gets ready to serve we see another flashback of Makoto Shimada reminding him that he should wait some of the allowed 8 second after the whistleblow to calm him. The referee gives the signal and we see Yamaguchi calm down and deliver his serve.
The ball looks to be out but curves downwards, turning into a service ace. The team celebrates him and Tsukishima notes that his serve wasn`t surprising, given all the work and practice he put into his serve. Yamaguchi's second serve curves once again hitting Mad Dog in the shoulder and scoring another service ace. Although the third serve is returned via an overhand hit Yamaguchi receives the ball and Tsukishima scores the point. Tsukishima hands Yamaguchi the ball back with a faint smile, who after a timeout from Seijoh hits his fourth serve. This time Yamaguchi decides for a more offensive approach by aiming for the top of the net, which gets him his third service ace. His fifth serve has a loose spin and doesn't change direction, but Asahi still scores a point off the returning ball. Even though his sixth serve turns out good, Seijoh returns it and scores, finally stopping Yamaguchi's 5-point streak. Outside he is complimented by the coach and his teammates and tells Hinata that he will score 10 points next time.
After a strong serve from Oikawa Yamaguchi compares himself to him, admiring his power and accuracy even during a tense situation.
In the final set he gets switched in once more, hitting another curving float serve, but Seijoh barely manages to pick it up and score. We see Oikawa internally being amazed by Yamaguchi's progress and Ukai compliments him once more, saying that it was a great serve that could only be stopped because of Seijoh's very strong play.
Yamaguchi grows into a reliable pinch server with his jump float serve. Early on, Yamaguchi began practicing the jump float serve technique, not wanting to be left behind by the other first years. Although attempting and failing the serve against Aobajōsai at a tight moment of the match, he works extremely hard to improve it. He is originally hindered by his lack of experience and weak-heartedness but, since then, has grown much more assertive and confident about his role.
Despite his skills as a server improved over time, his body control as a receiver is still lacking, resorting to body saves and unorthodox shots.
Height and reach, as of mid-November:
- Fingertip Height: 232 cm
- Jumping Reach: 315 cm (spike) / 300 cm (block)
- Jump Float Serve: This serve is Yamaguchi's main weapon and has helped out Karasuno in many clutch moments. His jump float serves can vary from skimming the top of the net to catching opponent off guard having to receive from further out before. Under the tutelage of Makoto Shimada, Yamaguchi increases the speed of his serve so that opponents have a harder time reading the trajectory. He also has worked on improving his aim and accuracy to target a specific player.
- Serve and Block Combo: This strategy involves Yamaguchi breaking the opponents' formation with his serves, thereby forcing players out from participating in offense. This would reduce the amount of information Tsukishima needs to process in order to put up an effective block. The two successfully use the serve and block technique in the match against Nekoma. 
- Kei Tsukishima: They have known each other since elementary school when Tsukishima saved Yamaguchi from some boys who bullied him by calling them pathetic. Despite thinking that he was included among the ones Tsukishima insulted, Yamaguchi still grew attached to him and set his goal to become "as cool as him".
Yamaguchi calls Tsukishima by a nickname, "Tsukki", though the latter doesn't seem to mind. Although Yamaguchi is generally a shy person, he follows Tsukishima whenever he's mocking other people and snickers along. Yamaguchi also doesn't seem to mind whenever Tsukishima snaps at him, and he even apologizes for his behavior. He seems to care for and admire Tsukishima a lot. This is shown during the match against Aobajohsai; every time a serve was directed to Tsukishima and he didn't receive it properly, Yamaguchi was freaking out on the sidelines, but after Tsukishima finally received one, he was shown crying in admiration. He also often brags about Tsukishima to other people, though the aforementioned stays silent or tells Yamaguchi to shut up. They are barely seen apart from each other and are even in the same class in school.
At first, it seemed like Yamaguchi was simply following after Tsukishima without being thoroughly acknowledged by him, but Tsukishima truly cared for him and viewed him as a friend. When Yamaguchi succeeded with his jump float serve for the first time ever, Tsukishima complimented him and pointed out his hard work to the other teammates. However, with the time they spent at Karasuno, they grew apart in terms of effort they put into their training: while Tsukishima did only what he needed to, Yamaguchi trained even after team practices to work on his float serve. The situation escalated in the summer training camp as Tsukishima still refused to put in any more effort because he didn't see a reason to. Yamaguchi, who was frustrated by Tsukishima's way of thinking, yelled at him for the first time ever to have pride in what he does instead of giving up like this. This changed Tsukishima, who even called Yamaguchi "cool" for the first time ever, causing their relationship to recover.
- Shōyō Hinata: Though Yamaguchi usually assists Tsukishima in mocking Hinata, Yamaguchi and Hinata develop a friendly relationship as the year goes along. Yamaguchi is always there to try to keep Hinata from getting into too much trouble. When Yamaguchi was at a loss of what to do with Tsukishima during the summer camp arc, he asked Hinata for advice.
During the Tokyo Nationals Arc, he and Hinata seem to have a better friendship. Yamaguchi even followed Hinata to gift shops and to watch the Fukurōdani vs Eiwa match. He was also present when Hinata ran into Kōrai Hoshiumi for the first time.
- Tobio Kageyama: Though originally hated by Kageyama because he aided Tsukishima in picking on the setter, Yamaguchi and Kageyama eventually developed mutual respect for each other. Whenever Yamaguchi was switched into games and succeeded with his jump float serves, Kageyama would compliment him.
- Hitoka Yachi: Yachi and Yamaguchi are good friends who get along well and can relate to each other. When Yachi first arrived with Shimizu to practice, Yamaguchi thinks of her as "cute." He's shy around her at first, but eventually they start to get closer. In the novels, Yachi comments that Yamaguchi is taller than she thought. Before their rematch against Aobajohsai, Yachi offers helpful advice to Yamaguchi on how to handle his anxiety but ended up becoming anxious herself. When Yamaguchi succeeded with his jump float serve, Yachi seems to be brimming with pride. Yamaguchi seems to have a small crush on Yachi, as he's seen blushing around her at times.
Karasuno Neighbourhood Association
- Makoto Shimada: Shimada is the one that taught Yamaguchi the jump float serve which became his forte. After watching Shimada play in the practice match against the Neighborhood Association, Yamaguchi went to his store and asked him to become his teacher. Since then, Yamaguchi often goes to Shimada Mart after closing hours to practice. Shimada acts like an older brother to Yamaguchi as well, often encouraging and cheering him on, and he also calls the younger boy by his first name. When Yamaguchi messed up during the Aobajohsai vs Karasuno match in the Interhigh, Shimada comforted him and motivated him to get back on his feet.
To himself, during his 3rd service Ace against Aobajohsai, Season 2 Episode 22
- Favorite Food: Soft, floppy french fries
- Current Concern: Whenever he thinks a cute girl has come over to talk to him, all they want to talk about is Tsukishima.
- His star sign is Scorpio.
- There has been debate over whether the dotting on his face is acne or freckles, but many believe that the specks are freckles.
- In Haikyuu!! Radio #22, Yamaguchi's voice actor, Soma Saito, described Yamaguchi with the word "freckles" in a guessing game with Uchiyama Kouki, Ayumu Murase, and Kaito Ishikawa.
- Since he's in Class 4 with Tsukishima, he must be smart; Classes 4 and 5 are college-preparatory classes in Karasuno. Although he himself has stated that he is terrible at English.
- His original reason for joining a sports club was so he could grow stronger. He chose volleyball specifically because the other sports clubs had "scary-looking guys".
- He is the only first year to not be a regular of the volleyball team.
- He is the second youngest of the first years.
- In the fourth instance of Haikyuu!! Radio, Yamaguchi's voice actor for the anime adaption, Saitō Sōma, was asked "What sort of person is your character, Yamaguchi?" to which he responded "Loves Tsukki very much."
- His seiyuu, Saitō Sōma, is also the seiyuu for Twelve, a character in the anime Zankyou no Terror. Number twelve is Yamaguchi's shirt number.
- In the english dubbing of the anime, he is the only first year, as well as one of few characters, refered to by his first name instead of his last name.
- He shares a birthday with Kenji Futakuchi.
- When asked about Yamaguchi's name origin, Furudate said, “He’s 忠 (loyalty), like a loyal dog!”
- 忠 is also how "Hachiko" is written. Hachiko is a famous loyal Japanese dog who also shares the same birthday as Yamaguchi.
- In Haikyuu's first popularity poll, Yamaguchi placed 15th with 1,993 votes. In the second, he rose to 7th with 6,561 votes.
- Tadashi (忠) - Loyalty; Devotion
- Yamaguchi (山口) - Mountain Entrance