|Name in Japanese||ギオ|
|Appears in||Anime, Manga|
|Voice Actor (Japanese)||Junichi Suwabe|
|Voice Actor (English)||Christopher Sabat|
Gio (ギオ Gio?) is a Dragon from the ISDA who is assigned to be Kazuki Tachibana's "partner" after Kazuki successfully resonated with Gio's Dragon Egg Form. However, despite being Kazuki's partner, Gio does not take orders from him, showing more concern for Toa, whom he states he was born to protect. Due to this, he is considered to be a failed experiment. His attachment to Toa seems to stem from the fact that he awakened early to Toa's cry when she first actualized in the series. After Toa runs away he assists Jin in finding her eventually ending up on Mars.
During a battle on Mars after seeing Akira killed and Machina falling to her death, his energy drastically increased while in his Dragon Form, and he created an explosion that caused the planet to burn; a phenomenon that can still be seen from Earth even a year later. During the time skip he lived with Toa and Jin and got a job. He seems to have developed an interest in cooking. Later, when he returns from his brief visit to Thanatos, his personality seems to have shifted, as he attacks his former comrades, and claims to be Thanatos's successor. However, he had only done this in order to ensure that Toa does not die. He would once again help his friends stop Thanatos, and in the end, he leaves Earth. Where he went to, is unknown.
Despite initially finding Jin to be a nuisance, he later forms a bond with him due to their shared feelings for Toa. After realizing how Jin and Toa feel for each other, he takes a supportive role, and tries to protect the two from danger. However, he still has lingering feelings for Toa, resulting in him feeling isolated from the two.
Gio is a sword type Dragon. He is able to create a black sword while in his Communicator form. His finishing attack as a Dragon is a passing slash with a sharp horn that he extends.
His name is derived from his code-number, "G10", which Kazuki misread as "Gio".
In the manga, he makes his first appearance as Kazuki's dragon partner.