| Name | Inui Sadaharu |
|---|---|
| Year | 3 |
| Height (cm) | 184 |
| Blood Type | AB |
| Birthday | June 3rd |
| Constellation | Gemini |
| Hand | Right |
| Cloth | |
| Shoes | Puma |
| Racket | Prince |
| Special Skill | Data Tennis |
| Quotes | I'm just here to take data |
| Favorite Subject | Physics |
| Favorite Color | Black |
| Hobby | Make vegetable juice |
| Description | The brain behind Seigaku's team. He takes data for all the games, including personal data for his rivals along with teammates. He's formerly known as Seigaku number 3 (right behind Fuji and Tezuka) - the data tennis man. But due to losing the Seigaku's regular selection matches in the beginning of the series (mostly because of Ryoma's appearance), he played Seigaku's manager for the first 50 or so episodes. |
- Sadaharu Inui (乾 貞治 Inui Sadaharu) is a highly intelligent player, who uses "Data Tennis." He constantly collects and analyzes data while in and outside of the tennis court in order to determine statistics, weaknesses, and other factors, and he is able to calculate the probability of certain shots being made during matches. While he collects data pertaining to tennis, he also collects personal pieces of data, such as favorite things, personal habits, and where they have been, which makes others feel awkward. In addition to his data tennis, Inui's play style includes his extremely fast serves the Sonic Serve and later the Waterfall Serve. Inui's data tennis style dates back to his elementary school days, when he learned it from his doubles partner Renji Yanagi.
- Inui was beaten by Ryoma, and then lost to Kaoru Kaidoh (who had also been beaten earlier by Echizen and was determined not to lose his spot) at the beginning of the series and became the team's manager. He uses his data to create exercise programs for the team. His most hated innovation would have to be his "Inui Juice" or "Penal Tea" (penalty), a disgusting health drink which is used as punishment. The contents of "Inui Juice" are unknown, but Inui is always coming up with new and "better" recipes. When the team went bowling, Inui's new invention "Aozu" first knocked out Kaidoh and even Fuji (who usually enjoyed drinking the "Inui Juice" or "Penal Tea") as well as the rest of the team. Even Inui himself falls victim to the "Aozu".
- Eventually, Inui is able to make it back as a regular by using the data he obtained over the time he was manager, losing to Kunimitsu Tezuka but beating Takeshi Momoshiro. While he's a very good singles player, he usually plays doubles with various partners, most notably his protegé Kaoru Kaidoh. His doubling with Kaidoh helped Seigaku overcome their problems with doubles teams (which Ryuzaki considered weak with only the Golden Pair as an effective team).
- One of Inui's most notable traits is his penchant to brew horrible vegetable juices (named "Inui Juices"), which he uses mostly in practice as punishment for players who fail the training menus. Only he and Fuji dare to drink.
