|Date of Birth||November 10|
|Height|| 179.5 cm (5' 10.7") - April |
180.0 cm (5' 10.9") - November
|Weight||63.0 kg (138.9 lbs)|
|Goal|| Practice more |
Be able to play in a match as a regular
Have a greater presence
|Likes|| Volleyball |
Soft, floppy french fries
|Occupation|| High School Student |
(1st Year, Class 4)
|Position|| Middle Blocker |
|In the Manga||The King of The Court|
|In the Anime||The Formidable Ally|
|Voice Actor||Sōma Saitō|
|English Actor||Cameron Bautsch|
Yamaguchi is a young-looking boy with an average build. He has short black hair, often portrayed as brown or even green with a flyaway piece of hair sticking up at the top. Back in middle school, he was teased for his freckles/acne 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, he tends to snicker along or join in with Tsukishima whenever he's mocking others.
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 Aobajōsai 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.
Jump Float Serve
Early in the series, Yamaguchi began practicing the jump float serve technique. Although attempting and failing the serve against Seijoh at a tight moment of the match, he worked extremely hard to improve it. Not even Nishinoya can receive his serves consistently. He made a very dangerous ace on the game against Wakutani High where the serve barely flipped over the top of the net and dropped on the opponent's zone, resulting in an ace and set point in the first set, but he was too nervous coming into the game anyway, and was scolded by an angry Keishin Ukai, but was spared after Chikara's plea. By the time Karasuno played against Aobajosai, Yamaguchi's jump float serve has managed to fool opponents since he no longer tried to serve right at the whistle. Under the tutelage of Makoto Shimada, his jump float serve can skim the top of the net to catch opponent off guard having to receive from further out before. He scored 5 points in a row while serving in the tournament.
As of mid-November:
- Fingertip Height: 232 cm
- Jumping Reach: 315 cm (spike) / 300 cm (block)
- 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.
- 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 in the first series of the anime.
- 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.
- 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.
- Tadashi (忠) - Loyalty; Devotion
- Yamaguchi (山口) - Mountain Entrance