• Peebo (ピーボ, Pībo?) - Peebo is the guardian of the Bio Particles, Bio Robo and Bio Dragon. She was built as an experimental robot when the Bio Particles were in development. She came to earth 500 years ago and showered five courageous people with the Bio Particles. Now that Gear has made its move, it is time for Peebo to summon descendants of the original five. She shows a great fear for Silva. In the last two episodes, she used herself to energize bio robo.
  • Bio Hunter Silva (バイオハンター・シルバ, Baio Hantā Shiruba?) - A robot from Bio Star programmed to kill anything with the Bio Particles. He was given half of the Bio Particles. He can also fire arrows from his elbow. He became maniacal and with his mecha, Balzion (バルジオン, Barujion?), helped destroy Bio Star. He armed himself with the bio killer particles (which killed Yellow Four I), but his shots were not able to kill any of the Biomen probably due to their upgrade, and used them to power up his robot as well. He is enemies with both Biomen and Gear. He killed Mason using the arrows that he fires from his elbows. He was killed when Balzion was defeated by a sudden charge of Bio Energy from the Bio Robo. English version name is Silver and his mecha is Bio Destroyer.
  • Shūichi Kageyama (蔭山秀一, Kageyama Shūichi?) - Thinking himself an orphan, named Kōichi Nakamura (中村 公一, Nakamura Kōichi?) (English version name is Sonny Satsuki), he learns he is in reality Shūichi Kageyama (English version name is Nicky O'Hara), the son of Doctor Man from whom the Black Prince is based from (actor Hidenori Iura plays both Prince and Shūichi roles). At first, Doctor Man tries to get him to join Gear, but Shūichi rejects Doctor Man. Eventually, Shūichi finds and joins Doctor Shibata (43-44). Later, he helps the Bioman ultimately defeat Gear. He manages to convince Doctor Man to help them stop the bomb that could destroy the whole Earth through the use of human emotions.
  • Professor Shibata (柴田博士, Shibata-hakase?) - A brilliant cybernetics and robotics professor who develops a "conscience circuit" for Gear's Mecha Clones. Later revealed to have a dual identity. Shibata is revealed to be Shirō's biological father. In episode 49, He used a Mecha Clone to communicate with Shirō. He died to save the other Biomen in Episode 50.
  • Brain (Buren) - A super-computer artificial brain developed by Doctorman in episode 14, to control the Mecha-Gigan Anchor Kans ; proving too intelligent, Brain eventually disobeys Doctor Man's orders after being taunted by Red One, and leaves the Mecha Gigan's cockpit to face the Biomen by himself ; he is then wounded and chased down by Gear's henchmen, only to be rescued by Pink Five who tries to teach him about human emotions. Eventually understanding the concept of "friendship", Brain ends up sacrifying his own existence to allow the Bio Robo to defeat Anchor Kans. His last words before dying were for Pink Five and the friendship she had offered him.
  • Miki - a special Mecha Clone developed by Doctorman to be coupled with Satan Megas in episode 43-44, Miki had the unusual appearance of a young girl in school uniform. As long as she existed, Satan Megas was able to re-assemble himself indefinitely, making him virtually invincible. After being implanted with Professor Shibata's conscience circuit, however, Miki felt guilt for the ravages caused by Gear, and resorted to self-destruct so the Bio Robo could defeat Satan Megas.