|Seidou High School - No. 14|
|Bats: Right||Throws: Right|
|Age||16 (debut) |
|Date of birth||05 June|
|Height||178 cm (5' 10")|
|Weight||72 kg (158 lbs)|
|Education||2nd Year High School (debut) |
3rd Year High School 
|Voice Actor||Miyake Takahiro|
Yamaguchi Ken is a student of Seidou High School. After the end of the summer tournament and the retirement of the 3rd-Years (Yuuki's generation), Yamaguchi was able to make it to the First-String. He was also formerly roommates with Miyauchi Keisuke.
Yamaguchi Ken likes to build up his body, he is very muscular and likes to weight lift.
He is the reserve 1st baseman of the first string.
Yamaguchi is a power hitter, who makes long hits and is capable of hitting a homerun.
He has a rivalry with Maezono since both of them play 1st baseman position, and they both make it to the first string at the same time.
His batting avg and power are similar to Maezono, and is one of the reasons he will not let it end with just being his reserve.
|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|