Sumiko Ozawa
The genius behind the G3 System. Her position within the G3 unit is the system's monitor engineer, which monitors the condition of the operator and the G3 suit during combat from the G-Trailer mobile command base. She was in constant rivalry with Toru Hojo. She is very glad when learning that Shoichi is Agito. In the series epilogue, she left the police force after the Overlord incident and moved to England to work at a university.
Mana Kazaya
Daughter of Nobuyuki Kazaya and niece of Professor Yoshihiko Misugi with whom Shoichi lives with. It is revealed she also possesses the Agito seed, as Tetsuya/Shoichi awakened her powers and eventually asked her help to resurrect Ryou/Gills.
Professor Yoshihiko Misugi
The man Shouichi lives with, as well as Ozawa's old college professor.
Taichi Misugi
The son of Yoshihiko Misugi.
Takahiro Omuro
He helps Ozawa at the G-Trailer mobile command base. Often the comic relief of the G3 team, he tends to be more immature than Hikawa and Ozawa, and is more carefree than the other two. In the series epilogue, he becomes squad leader of the G5 Unit.
Sakiko Mikumo
In charge of the O-Parts Research Department, her group researched the items from old long lost civilizations. By chance, she and her group found the puzzle that held the Overlord's DNA and unlocked it. With no idea of its true nature, she had the 30,000 old DNA synthesized, resulting with the Overlord of Darkness being reborn as well as the division being disbanded upon his escape. However, because the Overlord followed her, Sakiko was murdered by Anguis Femineus. As killing a regular human is considered a taboo among the Unknown, Anguis Femineus was controlled to commit suicide by the Overlord himself after that.
Ryuji Tsukasa
A member of the police force who was Hojo's senior partner, taking a bullet meant for him in the past that resulted in his hospitalization while his sister was murdered. Arriving to review the G3 Squad's abilities, he questioned their theories while dragging their name down the mud as a cover to kill Hisashi Hanamura, the man who murdered his sister Saori for breaking off their wedding and never being convicted of it due to lack of proof. Succeeding to make Hanamura's death look like the work of an Unknown with a tight alibi, Tsukasa confessed after Hojo tore it down and turned himself in.
Professor Nobuyuki Kazaya
Mana's father and Yoshihiko's step-brother. He is also Yukina and Sawaki's college professor. Dead prior to the series beginning, he is always depicted in Mana's flashbacks as a loving father, warning her not to tell anyone about her supernatural powers. However, he is actually a very ambitious man, desiring to prove to his step-brother that he could create a super-human. Obsessed with Yukina's supernatural powers, he conducts a series of experiments on her with Sawaki's aid. This eventually leads to his accidental death by the hands of Yukina. Ironically, his death was on the same day as Mana's birthday.
Aki Sakaki
Claiming to be a housekeeper sent by Professor Misugi, Aki was sent by her fellow Akatsuki members to investigate Shoichi, eventually claiming herself to be his highschool sweetheart when pressed to the way. She also encounters Ryo, to whom she denied being aboard the Akatsuki before forced to reveal the truth about it. However, before she could tell Ryo the full truth, having feelings for him, he was attacked by Hojo and his group. Believing Ryo to be dead, Aki's powers begin to manifest as she makes her way to Masumi and have him print out everything on the Agito Capture Plan and going after those involved. But before that, she encounters Tetsuya who accelerated her power's evolution. As a result, she became corrupted by it and started to use her psychic powers to murder those involved in the Agito Capture Plan while evading the Jaguar Lords. While attempting to kill Hojo, learning that Ryo was still alive, she was attacked by Panthera Rubeo. Though she escaped him with aid from Gills, Aki is ambushed by Pantheras Magistra who snaps her neck. By the time Agito found her dead body, Ryo arrived at the scene and assumed Agito had murdered Aki, starting a series of heated battles until the two could finally make peace.
Tomoko Miura
Age 29, she was among the passengers. Tomoko encounters Shouichi by accident, recognizing him as the young man she believed had died on the Akatsuki. She calls the Misugi residence to tell Shouichi to meet her tomorrow afternoon at East Park for the answers he seeks. But prior to their meeting, Tomoko was strangled to death by the Overlord himself. Overlord also revealed during conversation with Sawaki that during killing her, he feels an extreme heartache by killing his own child. Her death would cause the Overlord to retreat for a period of time to deal with this heartache.
Saeko Shinohara
Tomoko's best friend, Saeko lives with her big brother, an archaeologist. After the Akatsuki incident, she was traumatized to the point of being unable to interact with anything. But when she hear of the false legend of Sandouko Lake, she began to scuba dive for relics of the Jomon era that tell of an ancient civilization which worshipped an ancient Agito. To keep Saeko in that state of mind, her brother dumped the relics she found into the lake. When her special ability began to surface, Equus Dies attacks her. But during the fight between Gills and Dies, Saeko gets her leg stuck to seaweed and drowns.
Katsuhiko Sagara
Was awaken by Tetsuya, possessing pyschokinesis and regenerative powers. He managed to kill Gills. Attempted to trick Mana into believing she could not control her powers. However, Katsuhiko was murdered by Crustata Palleo.
Masumi Sekiya
A cynical woman and one of the passengers involved in the Akatsuki incident, ending up serving as a host to the El of Water until he gathered enough energy to leave her body, depleting her of her life-energy as a result.
Koji Majima
Came from a line of doctors, befriended Mana and idolized Kino. When Ryou was injured after a fight with Another Agito, Koji was told by Tetsuya/Shoichi to give Ryo his Agito seed in order to save his life. As he gave up his power, Ryou was not only completely healed, but was able to access Exceed Form. He is the only surviving member of the Akatsuki by the end of the series. Other people who were in the Akatsuki incident were Jun Tachibana, Masahide Takashima and Kazuo Ashihara.
Tetsuya Sawaki
The real Shouichi Tsugami is a man resurrected by the Overlord due to his passive involvement in the death of the first Agito, Yukina Sawaki. In reality, he was romantically involved with Yukina and tried to stop her from committing suicide, but he ultimately allowed her to plummet to her death. Soon after, he also committed suicide as he could not stand the guilt over Yukina's death. However, the now-grown up Overlord resurrected him and gave him some of his power, enabling him to accelerate the Agito seed evolution. However, he turned his back on the Overlord as he realized the world needs more people who can become Agito. Tetsuya eventually managed to redeem himself by saving Kana, before the Overlord granted him eternal rest to view mankind's future alongside him.
Yukina Sawaki
Sister of Kamen Rider Agito. A young psychic woman who committed suicide after discovering she was becoming the very first Agito. She was involved in a paranormal research conducted by Professor Kazaya at Jyohyoku University. These experiments results were severe traumas on her which led her to kill Kazaya unconsciously. She left behind a younger brother, Tetsuya Sawaki, who would later become Kamen Rider Agito.
Series:  Kamen Rider Agito