Higashio, often referred to as Director Higashio, is the lead director of the Bone Research Facility located in Melbourne, Australia. He is a man of approximately fifty years of age with black hair and brown eyes.

His personality is marked by a gruff and often unprofessional exterior. He is a notorious heavy drinker, frequently seen suffering from hangovers and surrounded by alcohol, which can make him appear grumpy and irritable to those who first meet him. Despite this seemingly careless attitude towards his own well-being, he possesses a deep and serious understanding of the dangers associated with the Bone Cards and the process of making a Majin descend. When the young adepts first visit him in Melbourne, he confronts Shougo Ryuujin directly, shaking him and sternly warning the group about the life-threatening risks of forcing a descent, emphasizing that it could lead to the adept's death.

Higashio's history and motivations are deeply rooted in his past experiences as a field researcher. Four years prior to the main events of the story, he led an excavation project to uncover ancient stone bone tablets. During this time, he was briefly taken hostage by Victor and Gregory, but managed to turn the situation around, ultimately saving their lives after a raid by a hostile group left them gravely injured. It was during this same incident that the Tiger Bone and Wolf Bone first responded to Victor and Gregory, transforming them into bone warriors. Higashio continued his research, eventually unearthing the Leo Bone a year later. These events established a powerful, if complicated, bond between the director and the two brothers. Years later, he arranges for Victor and Gregory to repay their life debts to him, first by leaving behind data on how to defossilize Dragon Bone, and then by teaching the Earth's adepts how to unlock their iron transformations.

Throughout the main storyline, Higashio serves as a supporting figure from the research facility, initially helping to fix the damaged Dragon Bone. However, his role becomes more complex when he is revealed as the lab's traitor, though his motivations are not aligned with the alien invaders. Luke deduces that Higashio is the only one capable of removing cards from the lab, leading to this discovery. In truth, Higashio is secretly cooperating with Victor and Gregory, a decision rooted in his past and his own convictions rather than outright betrayal of humanity. In the series' later stages, his character further develops as he seeks out representatives from the alien world Nepos Angelis, not as an enemy, but in hopes of building a different kind of understanding. His actions demonstrate a man willing to operate outside the established rules, driven by a complex network of past debts, personal loyalties, and a potentially broader vision for resolving the conflict.

While Higashio does not fight as a bone warrior himself, his authority and access as the facility's director are his primary functions within the narrative. His most notable ability is his profound knowledge of the bones, their fossilization, and the mechanics of the Majin, which he uses to both warn and assist the main characters. His key relationships are with the members of the Melbourne lab, including his colleague Leonard, and most significantly with the wandering warriors Victor and Gregory, whose lives he saved and to whom he remains connected by a powerful sense of obligation and shared history.