St. Rudolph
Hajime Mizuki is more of a manager for St. Rudolph, he's like Seigaku's Data Specialist, Inui, when it comes to data gathering. He's also a player for St. Rudolph, Singles 2 specifically. He's the one who taught Yuuta his special move, Twist Spin Shot which gives lot of burden to his arm and shoulder. All through out the anime, Mizuki shows keen interest to both Yuuta and Syuusuke although, no one knows why.
Fuji Yuuta is Syuusuke's younger brother and was originally from Seigaku, but due to the popular reputation of Syuusuke, Yuuta was always ignored and commonly known as "Fuji's younger brother". Therefore, he switched schools and went to St. Rudolph. He's left-handed or southpaw player like Ryoma and Tezuka. His special moves are Super Rising and Twist Spin Shot. Due to his special moves, he's also known as the "lefty-killer".
Yanagizawa Shinya is a doubles player with Kisarazu (Atsushi). He's very loud and obnoxious. He always adds a "da ne" on most of his sentences as a sign of speech mannerism.
Kisarazu Atsushi is a doubles player with Yanagizawa. He's more reliable than his doubles partner and tends to be the opposite of Yanagizawa. He's the quiet type. He also has a brother which would appear in the later part of the anime.
Kaneda and Akazawa are paired once for doubles 1 to fight Seigaku's Golden Pair. Akazawa is originally a Singles player but because of his illusion technique that brings out Eiji's weakness, he was put to doubles and team up with Kaneda (who's like a single groupie of Akazawa).