| Seidou High School - No. 3|
|First Baseman (high school)|
|Bats: Right||Throws: Right|
Leader (リーダー Rīdā') (by Sawamura)
|Age||17 (debut) |
|Date of birth||8 October|
|Place of birth||Tokyo|
|Height||180 cm (5' 11")|
|Weight||75 kg (165 lbs)|
|Family||Yūki Masashi |
|Education||3rd Year High School (debut)|
|Skills||hits powerful curve balls and most signature pitches of aces|
|Manga||Act I - Chapter 14|
|Anime||S1 - Episode 4|
|Voice Actor||Yoshimasa Hosoya|
|“||Even when times are at the hardest, don't let it show on your face. If the captain is shaken, the team will waver.||”|
— Yuuki to Miyuki in Succeed
Yuuki Tetsuya was the captain and first baseman of the Seidou High School baseball team. He grew up in Tokyo Metropolis and graduated from Akadou Junior High. Observing the team's discipline, Yuuki decided to enroll at Seidou. While he was in junior high, he was not given much opportunity to play because of his small build despite his strong fighting spirit.
Yuuki is the most composed core member of the team who greatly supports his teammates with his straightforward and calm personality. He is dedicated to enhancing his batting and fielding skills and leads the team through his performance. Even after retiring, he was happy to help the new team with their practices.
He and his vice-captain Isashiki are the team's senior members with high senses of responsibility. Right after Tanba's injury, they were the first people challenged by Kataoka to renew the team's motivation. Their response rightly brought back the team's spirit.
As the team's captain, Yuuki leads them through his performance. He knows his role as the fourth batter and does his best to meet everyone's expectations of a captain. Yuuki has a very strong presence, especially to Mei Narumiya. He is the only member of Seidou whom Narumiya seriously faced during the finals.
Yuuki was not an outstanding player from the start. Although he claimed to have experience and expertise (out of confidence) in fielding, Yuuki struggled in his first year along with Isashiki and the others.
In order to cope with his weakness, he trained himself vigorously in and out of the field. He swings at least 500 a day in order to strengthen his batting skills and inspired his batchmates to train as much as he did. His training soon paid off as he was the first in his batch to produce results by getting a home run in their first practice game. His steady performance and skills impressed his teammates and opponents alike, so much so that his teammates unanimously voted him to become the next captain.
He later attends Meijin University and is a first year player of the university's baseball team. He participates in a practice match against the Tokyo All Stars team where he faced his high school friends and foes such as Miyuki and Narumiya.
Relationship with other charactersEdit
Isashiki and Yuuki were first rivals upon entering Seidou, but Yuuki was Isashiki's first real buddy and inspired him to practice even more, especially in batting. When Yuuki became the captain, Isashiki was appointed as vice-captain to support him. Isashiki is usually the first one to notice Yuuki's sudden change of moods (resulting from his intense aura).
Miyuki is Yuuki's shogi buddy. Even though Yuuki always loses, he never gives up playing (which is attributable to his determination). He is one of the seniors who often hangs out in Miyuki's room. On field, these two rarely have casual communication which shows their trust in each other. Yuuki was also the one to recommend Miyuki as the next captain; even though the pressure on the catcher would be great, Yukki believed he could lead the team.
During Yuuki's first year, he and the rest of his year are called 'the hopeless year.' But as time passes, Coach Kataoka noticed their determination on and off the field and became stricter than usual in training. Yuuki's hard work paid off after a great home run during a practice game in their second year and Kataoka was impressed. He then supported the seniors' unanimous decision in appointing Yuuki as captain, saying to him, "I don't need you to handle everything in the huge team perfectly. You just need to lead everyone with your performance."  Coach Kataoka gives great credit to Yuuki's performance on the field; occasionally, he tells the team to observe Yuuki and learn his responses to difficult offensive situations. Yuuki, in turn, has very high respect for the coach and decided to take a similar path to him. He rejected the opportunity to go pro and instead decided to attend the university Kataoka graduated from so he can come back to Seidou later as a coach.
Yuuki and Harada converse pleasantly during the Seido vs Yakushi match, talking about the current situation of their respective teams. Yuuki recommended Miyuki as captain due to the fact that Seido lost to Inashiro whilst Harada was captain and catcher; thus, Yuuki wanted Miyuki to be a captain that could surpass the level of Harada. They both seem equally shocked to finding out that Miyuki was injured during the match.
SkillsEditAs someone unanimously voted captain by his seniors and called an "unshakable pillar" by his teammates, Yuuki is the most reliable member of Seidou's baseball team. He has an outstanding and intimidating presence just by standing in the batter's box, usually symbolized by his aura. Other schools are very cautious of him as he is able to hit any kind of pitch; as a result, he is often intentionally walked by his opponents.
Batting: As the fourth batter, Yuuki is aware that hitting cleanup requires an exceptional level of talent and the ability to deliver big hits in important situations (such as the bases being loaded with two outs). On top of being a slugger, he is able to successfully cope with every type of course or pitch that comes his way, and the team scores often when he's at bat. His mental strength in critical situations is also very strong. Yuuki, among all team members "exudes the right aura" when it comes to baseball. One unique training he does is "image batting," and all that is left is hitting real balls during the game.
He was the only batter who hit Narumiya's pitches during the Seidou vs Inashiro game when he was still a second year. Narumiya is well aware that he is the team's key player who needs to be shut down when at bat and therefore goes all out when facing him. During the Summer Tournament, the two had another face-off wherein Yuuki was struck out twice before he finally hit 2-run RBI with the bases loaded, giving Seidou temporary relief during the defense.
Narumiya Mei aside, Yuuki was never struck out without a fight. He is regarded as the team's best and steady clean-up hitter. During games, Yuuki has the most reliable offensive performance who hits with instinct and experience.
Note that this data is based on the official guidebook!
- Tetsuya ranked 9th in the first Official character popularity poll. 
- He has respect for coach Kataoka and Yorozuya Kinnosuke
- He has a younger brother in his third year of junior high school, Yuuki Masashi, who also decided to go to Seidou for high school
- He strongly recommended Miyuki as the next captain because he believed that Miyuki was most fit to lead the team.
- Rankings from the guidebook: 
- Yuuki has the best fighting strength
- He is fourth in stamina - his time for 10 km is 36 min 40.17 seconds
- Fourth in ball contact
- Favorite Food: Pickled plum rice with green tea, soba 
- Favorite Subject: Japanese History, Classical Literature 
- Apart from baseball, he likes playing shogi; however, he's not very good at it. 
- His favorite historical drama is Kozure Ookami. 
- After graduating from Seidou, he began attending Meiji University, Kataoka Tesshin's alma mater.
- Yuuki (結城) - Forming Castle
- Tetsuya (哲也) - Sage/To Be Wise
- "We need to get stronger. For all those who weren't chosen." - to Sawamura 
- "Without doubt, we'll let you stand on the mound again." - to Tanba
- "It's not just Raichi. They have a monster of their own as well." - Sanada Shunpei 
- "Casual and natural. An irritating batting posture." - Osaka Kiryu's catcher 
- "No, I don't remember what I hit. By the time I noticed I was already on second base."  - after hitting Narumiya's changeup
- "I don't really want to say this, but there's no way I can win against him, and only him! That's all!" - Isashiki 
|Seidou High School|
|Miyuki Kazuya • Maezono Kenta • Kuramochi Yōichi • Kawakami Norifumi • Asou Takeru • Nakata Ataru • Ono Hiroshi • Higasa Shōji • Seki Naomichi • Yamaguchi Ken • Kijima Rei • Kawashima Kengo|
|Sawamura Eijun• Furuya Satoru • Kominato Haruichi • Kanemaru Shinji • Tōjō Hideaki • Kaneda Tadahiro|
|Yui Kaoru • Yūki Masashi • Okumura Kōshū • Mogami Takeshi • Asada Hirofumi • Seto Takuma • Kuki Yōhei
|Former players||Yūki Tetsuya • Tanba Kōichirō • Kominato Ryōsuke • Masuko Tōru • Isashiki Jun • Miyauchi Keisuke • Sakai Ichirō • Kadota Masaaki • Kusunoki Fumiya • Takigawa Chris Yū • Azuma Kiyokuni
|Managers||Fujiwara Takako • Umemoto Sachiko • Natsukawa Yui • Yoshikawa Haruno
|Staff||Kataoka Tesshin • Ochiai Hiromitsu • Takashima Rei • Kazuyoshi Oota|