Seto has medium length brown hair (with red highlights) that reaches down to his chin. He is first seen wearing red glasses, a yellow button up shirt, a white, long-sleeved undershirt, blue cargo pants and a white hat.
He was a third year junior high student, and was formerly a shortstop of the Daikyou Senior League. The specific team he was on is unspecified.
Seto and Okumura attended Daikyou Senior and came to watch Seidou take on Teito in the Fall Tournament when deciding which high school to enroll to. After enrolling at Seidou it's obvious that he sincerely cares about Okumura and often looks out for him, telling him that he doesn't have to push himself so hard.
Seto is a player with good leg and seems to be adept at stealing and putting pressure while on bases. His records and effectiveness are not yet available but Kuramochi once noted that Seto's base stealing techniques demonstrated he must have had an extensive amount of training to be able to employ.
- Until the start of Act II, he was always seen wearing a beanie.
- During the introduction of the first years, he is seenwithout his beanie for the first time.
- He is very confident in his legs.
- He calls Yuuki Masashi and Yui Kaoru "iron stomach monsters".
- Seto (瀬戸) - Port to the Rapids
- Takuma (拓馬) - Supporting Horse
- "Koushuu, whose pitch do you want to catch?" - to Okumura
- "Everyone here is such a sore loser." 
|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 • Shirasu Kenjirō • Mimura Ryōta • Watanabe Hisashi|
|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|