Boichiro Yamato is a character from the light novel and anime series Demon King Daimao, serving as a primary antagonist who later becomes a supporting figure. His background is deeply rooted in tragedy and a long-term mission to alter the course of history. He is a time traveler, having journeyed from hundreds of years in the future to the era in which the story takes place. During his original time, his teacher revealed to him the nature of the Law of Identity and the intention of the God of the Old Planet to destroy mankind. Driven by this knowledge, Yamato developed the technology to break through the barriers of time and space, becoming a lone traveler determined to prevent the catastrophic future he knew.

In terms of personality, Yamato is portrayed as calculating, ruthless, and intensely focused on his goals. He holds a high-ranking position as the Director of the Cabinet Intelligence and Magic Office, often shortened to CIMO8, and is a member of the Imperial Public Safety Committee. He is willing to commit murder or any other necessary act if it serves his ultimate ends, displaying a cold and pragmatic side to his character. Despite this ruthlessness, he is identified as a rare example of a non-evil antagonist; his primary motivation is a sincere desire to protect the world and change the destructive relationship between gods and humanity, freeing both from a corrupt system imposed by the High Priests. This mission leads him to seek control over Kena Soga, whom he refers to as the "principle of identity," believing her unique abilities are key to ruling over the gods themselves.

Yamato's role in the story is that of a formidable antagonist to the protagonist, Akuto Sai. He is initially shown attempting to have Kena Soga assassinated before intervening personally to capture her for his own plans. His conflict with Akuto is direct and physical, as Yamato's power far surpasses that of the young demon king at their first encounter. He is also connected to the past, having sealed the black dragon Peterhausen and bestowed the Brave suit to Hiroshi Miwa's grandfather over a century before the main events. He has a relationship with a character named Rimu, which is the reason he waited for Kena Soga since her birth and gave her a distinct hair decoration. He also has a mutual acquaintance with the headmaster of the Constant Magic Academy, who eventually intervenes in one of Yamato's battles.

Yamato undergoes development that shifts his role from a primary villain to a supporting player. Initially a major threat with the power to easily overpower Akuto, his plans are eventually thwarted. Following a significant defeat, he is stated to have disappeared into another dimension of time and space. However, his existence continues to have impact, as his soul persists even when changes to history erase his original future. In later stages of the narrative, he exists within a metaphysical afterlife, where he is considered a being with god-like status and influence comparable to other powerful characters.

Notable abilities are a defining feature of Boichiro Yamato. He is an extraordinarily skilled swordsman with centuries of combat experience. His primary weapon is a large greatsword, which he can also use for flight. His most powerful technique is called the Hodgson Type Complete Severing, an attack that cuts through space itself. This technique ignores distance, cuts at a precision higher than a molecular level, and can bypass any barrier by severing the dimension. Beyond his combat skills, he invented and possesses an array of powers related to his nature as a time traveler. These include the ability to manipulate and travel through time, teleport, store weapons in a separate pocket dimension, and send opponents to different dimensions. He also demonstrated the ability to seal powerful entities like the dragon Peterhausen.