One day, the MTB team "Sharktooth" created by the Samejima brothers, who are also in the same elementary school, are challenged to an MTB battle for the "X-Zone," a place that holds memories of their dead father. On Sunday, while Shou and the leader Gabu were competing, black smoke enveloped the area and they were warped into a mysterious world. An adult MTB rider appears in front of the bewildered group and announces that they are in the X-Zone where they must compete with him in the Idaten Battles. In order to return to the original world, they must win the Idaten Battles and collect 10 gold emblems.
Kakeru is one of the main characters in the series. His main job in their team is to fix Shou, Makoto and Ayumu's bikes and also to change their bikes' gears whenever they are going to have an Idaten Battle.
Kyoichi Shido is Makoto Shido's elder brother. He is amazingly talented at everything, especially mountain biking. He is very protective towards his sister, also being a serious person. In the first few episodes, he used to follow Makoto, Shou, Kakeru and Hosuke but he always kept his distance. His MTB is Thunder Emperor and he is really an awesome unbeatable and impeccable rider, being a trial bike champion.
Yuki is a mechanic who is one of the protagonists of the anime. She is actually a princess from a very respected family. She is an expert mechanic and helps Shou and co. on various occasions. Arthur and Yuki have helped protect the secrets of the X-Zone. She has been wanting to be a mechanic from her childhood. She is Hosuke's granddaughter.
Koei is a ninja rider hired Gabu Samejima and was a member of Team ST. It is later revealed that he did so because he could not afford a doctor for his sister, Kiku. Once Kiku fell in Gabu's clutches, Shou had to help rescue her. He rides the Idaten Bike Aero Scissors. His special move is the "Ninjutsu Hurricane" by which he can create a hurricane around him.
Ayumu Yamato is Shou's younger brother. He joins the group during their return to the X-Zone. Ayumu used to behave like a maniac and ride without any control when riding MTB's until Koei taught him about control. He rides the Idaten bike Imperial Dragon.
Takeshi Yamato is Shou's father. While falling off his bike in an accident, he was transferred to the X-Zone to repair Imperial X. He had built Flame Kaiser, Thunder Emperor, Neptune, Imperial Tiger, Imperial Dragon, Aero Scissors, Hammer Head and Bloody Fang as well. Possessed by an ancient evil, he rode Imperial X whose attack was Even's Destruction. He defeated Flame Kaiser and took away its emblem but lost in the rematch where Shou rode with the combined forces of Bloody Fang, Thunder Emperor, Aero Scissors, Hammer Head, Imperial Dragon and Neptune. He made the Idaten Bikes to restore and maintain peace in the X-Zone and protect Imperial X.
Gabu Samejima is the strongest MTB Rider along with Kyoichi Shido. He rides the powerful Idaten bike, Bloody Fang. Gabu and Taiga Samejima are the leaders of Team Sharktooth aka Team ST. He goes to the same school as Shou, Makoto, and Kakeru. When Team Sharktooth arrived in the X-Zone, Gabu became the dictator of X-City after overthrowing it's mayor.
Taiga Samejima (鮫島 大牙, Samejima Gabu)
Voiced by: Toshiyuki Kusuda (Japanese); Steve Staley (English)
The older brother of Gabu who serves as his second-in-command of Team Sharktooth.
Four Kings (四天王, Shiten'nō)
Kiyoshi (キヨシ)Voiced by: Yū Urata (Japanese); Brian Beacock (English)
Mitsuru (ミツル)Voiced by: Kōta Suzuki
Seiji (セイジ)Voiced by: Hiroshi Shimozaki
Mantarou (マンタロー)Voiced by: Takehiro Hasu
Kiyoshi, Mitsuru, Seiji, and Mantarou are four MTB riders that are the members of Team Sharktooth.
Jackal is a ship captain who is a member of Team ST. He and his crewmen challenged Shou when Shou was on a ship to X-City. They did get away with some of Shou's Emblems at the cost of Captain Jackal's ship and handed them to Gabu and Taiga.
Yoko and Rika are two sisters who are resort tycoons in Gold Celebresort City and members of Team Shark Tooth. Yoko is a MTB rider while her sister Rika is a mechanic.
Mr. Teacher (ミスターティーチャー, Misutā Tīchā)
Voiced by: Ben Takada (Japanese); Kirk Thornton (English)
A teacher-themed biker in a school theme park and member of Team ST.
"The Terrifying Dark Emblem" Transliteration: "Kyōfu no dāku enburemu" (Japanese: 恐怖のダークエンブレム)
Jun Takahashi
Fumiyo Sakai
June 17, 2006 (2006-06-17)
38
"Gabu's Temptation, Flame Kaiser in Big Trouble!" Transliteration: "Gabu no yūwaku, Fureimu Kaizā dai pinchi!" (Japanese: 牙舞の誘惑、フレイムカイザー大ピンチ！)
Takashi Andō
Kiyoko Yoshimura
June 24, 2006 (2006-06-24)
39
"Incandescence! Imperial DG VS Aero Scissors" Transliteration: "Hakunetsu! Inperiaru DG VS. Earo Shizāsu" (Japanese: 白熱！インペリアルDG VS. エアロシザース)
Hajime Tanaka
Kōji Miura
July 1, 2006 (2006-07-01)
40
"Bad Bacteria in the Nanashi Forest" Transliteration: "Nanashi no mori no akudamakin" (Japanese: ナナシの森の悪玉菌)
Daisuke Takashima
Natsuko Takahashi
July 8, 2006 (2006-07-08)
41
"Arthur's Challenge! The Road to the Phantom Island" Transliteration: "Āsā no chōsen! Maboroshi no shima e no michi" (Japanese: アーサーの挑戦！幻の島への道)
Shunsuke Tada
Kiyoko Yoshimura
July 15, 2006 (2006-07-15)
42
"Idaten Biker Gathering! The Decisive Battle Against Team X!" Transliteration: "Idaten baiku daishūgō! Chīmu X to no kessen!" (Japanese: 韋駄天バイク大集合！チームXとの決戦！)
Yoshihiro Mori
Shinzō Fujita
July 22, 2006 (2006-07-22)
43
"Shou VS Shidou! Battle For the Soul!" Transliteration: "Shō VS. Shidō! Tamashī o kaketa batoru!" (Japanese: 翔VS.獅堂！魂を賭けたバトル！)
Yoshimichi Hirai
Fumiyo Sakai
July 29, 2006 (2006-07-29)
44
"Shocking Reunion! Imperial X Appears!" Transliteration: "Shōgeki no saikai! Inperiaru X shutsugen!" (Japanese: 衝撃の再会！インペリアルX出現！)
Hajime Tanaka
Fumihiko Shimo
August 5, 2006 (2006-08-05)
45
"The Second Island Appears! The Beginning of World Collapse" Transliteration: "Daini no shima arawaru! Sekai hōkai no hajimari" (Japanese: 第二の島現る！世界崩壊の始まり)
Yasutaka Yamamoto
Kōji Miura
August 12, 2006 (2006-08-12)
46
"The Great Assault! Team X VS Imperial DG" Transliteration: "Daishūgeki! Chīmu X VS. Inperiaru DG" (Japanese: 大襲撃！ チームX VS. インペリアルDG)
Jun Takahashi
Natsuko Takahashi
August 19, 2006 (2006-08-19)
47
"Legendary Training Ground, Shou's Special Training!" Transliteration: "Densetsu no renshūba, Shō no tokkun!" (Japanese: 伝説の練習場、翔の特訓！)
Daisuke Takashima
Kiyoko Yoshimura
August 26, 2006 (2006-08-26)
48
"Miraculous Power! New Special Moves Burst Forth" Transliteration: "Kiseki no chikara! Shin hissatsuwaza sakuretsu" (Japanese: 奇跡の力！新必殺技炸裂)
Kenichi Matsuzawa
Shinzō Fujita
September 2, 2006 (2006-09-02)
49
"Flame Kaiser vs. Team Idaten Rider" Transliteration: "Fureimu Kaizā VS. Chīmu Idaten Raidā" (Japanese: フレイムカイザーVS.チーム韋駄天ライダー)
