Professor Ichiro Horiguchi
A famous space archaeologist whose analysis of some ancient crystals lead him to discovering the secret of the Gransazers, the Chou Seishin, and the Gransazer War. Many have sought this knowledge. His assistant, Mika, was awakened as Sazer Mithras. Her new partners, Ken and Tenma, were awakened as Gransazers later. He guides the Sazers by giving them information and leads.
Atsushi Misonogi
Although he is a bureaucrat, he is also very mysterious benefactor to Dr. Horiguchi's Gransazer research. Eventually, Misonogi reveals himself to be head of the Department of National Defense, using Horiguchi to track down the Gransazers for his country's gain. But after seeing the severity of the alien threat, Misonogi decides to support the Gransazers in anyway he can.
Masaki Wakui
Ai Uozumi's long lost father, who throughout Ai's childhood, he's only known by the name Dr. Bear. He led the team which repaired the Guntroller.
Souchiro Okita
He leads the strike team which assists the Sazers during battle. He also commands the robot Youhi using a special head piece.
Luka
Being of planet Marius with the power to give her lifeforce to others, Luka was sent to Earth by Belzeus to unknowingly unseal the Bosquito, summoning Gig Fighters to hold the monster off until Tarius arrives. After seeing that the Gransazers were nothing like the Bosquito and Tarius resolve to protect the Earth, Luka questions her actions and Tenma convinces her to leave Warp Monarch. However, in the end, Luka sacrfices herself to save Tenma's life. She appeared in Episodes 42-43.
Yuuhi
The Type-05 GS Assist Robot Yuuhi was the result of the JSDF reverse engineering DaiLogian so they can support the Gransazers' Chouseishin. Remote controlled by a voice-command headgear, the Yuuhi is launched from an underground bunker. It can access numerous weapons, a 120-mm dual cannon as well as two arrays of six missile launchers each. Prior to the final battle, Yuuhi was broken into pieces after fighting Troius. It appeared in Episodes 28-48.
Type-05 GS Assist Tank "Asahi"
Asahi is Yuuhi's support mecha. It vaguely resembles an M4 Sherman.
Jado
Jado belongs to the Stonian race of Planet Stone, who were chosen by Warp Monarch to attack Earth using the Mad Stone, a bomb-like rock of plutonium that the Stonians left on Earth ages ago. Refusing to let Earth be destroyed, Jado went to Earth to obtain the Mad Stone, taking over the body of Takumi Sawashima, An old friend of Ryouko from her college who died on his way to Tokyo after returning from Africa. But as a result of being forced to keep his host alive, Jado is weakening to the point that he would eventually die. Once Ryouko gives him the Mad Stone, the Stonian assigned to destroy Earth attacked him to regain the Mad Stone. Soon after, Takumi regained control over his body long enough before he and Jado leave Earth with the Mad Stone, detonating it in deep space and instantly vaporized.
Freedo
Freedo is an Intergalactic cop from planet Ajyante sent to kill Kriminal for his partner's sake. Fatally wounded, Freedo entered the body of Jin's friend Shinji to continue pursuit with Jin forced to partner with the alien to ensure Shinji's safety and help. Once Kriminal is dead, Freedo leave Shinji's body and departs into the afterlife.