Ido, the central figure of ID-0, first appears as a blue I-Machine, a type of humanoid excavator mecha, with no physical human body and no memory of his past beyond the last seven years. He is an Eternal Transmigrant, a person who has permanently transferred their consciousness into an I-Machine, a practice that is illegal and heavily stigmatized. Before being picked up by the crew of the excavation ship Esca Bate, he was imprisoned in this mechanical form aboard a prison ship for roughly two decades. Having no identification data of any kind, he was named Ido by his new captain, a name derived from his unique ID number, ID-0.

On the surface, Ido projects a personality that is stoic, taciturn, and often sarcastic. He is an exceptionally skilled excavator, possessing a calm, calculating demeanor that can make him seem cold or even ruthless. He has stated a philosophy of abandoning even comrades if they no longer serve a purpose or show a chance of survival. However, his actions consistently contradict this harsh outward attitude, revealing a deep-seated loyalty and protectiveness towards those he works with. He has risked his own existence on multiple occasions, such as diving alone into lava to rescue a fellow crew member or self-destructing his I-Machine body to protect the group, earning him their profound trust. This contrast defines him as someone who is cool on the exterior but possesses a passionate and caring interior.

Ido’s primary motivation throughout the story is the recovery of his lost identity. Initially, he seems to have accepted his amnesiac state out of a sense of futility, but this changes when a mysterious cat-eared girl named Alice is discovered within a large ore deposit. Physical contact with Alice triggers flashes of his suppressed memories, reigniting his desire to discover who he truly is. As the crew of the Esca Bate becomes entangled in a larger conspiracy involving the enigmatic ore known as Orichalt, Ido’s personal quest becomes inextricably linked to the survival of his comrades and the fate of humanity.

In the story, Ido serves as the keystone of the Esca Bate crew, a small company of outcasts and Eternal Transmigrants. His most critical relationship forms with Maya Mikuri, a young student whom he rescues. She becomes a viewpoint character for the audience, and through her eyes, Ido’s mysterious nature and the world’s rules are explored. Another pivotal relationship is with the silent girl Alice, whose mysterious connection to Orichalt acts as a catalyst for his memories. His past is deeply tied to his former colleagues, Jennifer Record and Adams Forte Chevalier, with the latter being the man who erased his memories and stole his original human body.

Ido undergoes significant development as he reconciles his current identity with his terrifying past. It is eventually revealed that before losing his memory, he was Dr. Kane Arisugawa, a genius but arrogant and psychopathic scientist who helped develop the Mind Trance System that allows consciousness transfer to I-Machines. As a scientist, his methods were inhumane; he callously used the desperation of a mother to further his research on Orichalt, an act that led to his betrayal by his colleague Adams. However, after regaining these memories, Ido no longer identifies as the ruthless Kane Arisugawa. Having lived as an excavator, he has forged new bonds and a new sense of self. Ultimately, he consciously chooses to remain Ido, the excavator and loyal comrade, over reclaiming the life of his former self, even sacrificing his chance at a human body to save Alice and his friends.

Regarding notable abilities, Ido is an accomplished excavator with a style that is both aggressive and precise. True to his I-Machine’s ninja-inspired design, his primary weapons are a series of beam kunai, which he wields in both melee combat and as throwing projectiles. He also possesses a built-in function that allows him to concentrate energy on his arms to generate intense heat, which is powerful enough to melt solid bedrock for excavation purposes.