Daigo is the lord of the Ishikawa region and the biological father of the protagonist, Hyakkimaru. His story begins sixteen years before the main events of the narrative, when his territory was suffering from famine, disease, and constant warfare. In a desperate bid to gain the power needed to save his land and secure his own ambitious legacy, Daigo made a pact with a group of demons. He promised them anything they desired in exchange for prosperity. The demons accepted, and when his first son was born soon after, the child was collected as the price: the baby was born missing numerous body parts, including his limbs, eyes, ears, nose, and skin.

Daigo’s personality is defined by immense ambition and a ruthless, pragmatic worldview. He is a man who believes that the ends justify any means, and he is willing to sacrifice anyone, even his own family, to achieve his goals of power and a prosperous domain. After the demonic pact, he displays little to no remorse or paternal affection for his mutilated firstborn, immediately ordering the infant to be disposed of. Instead, he focuses on his second son, Tahomaru, whom he raises to be his heir. Daigo is cold and manipulative, keeping the truth of his pact hidden from his family and subjects. He maintains a public facade of a great and benevolent lord who vanquished evil spirits, while privately he is calculating and willing to commit horrific acts, such as ordering the massacre of innocent villagers and children, to maintain his power.

Daigo’s primary motivation is the preservation and expansion of his own power and the prosperity of his land, which are both now directly tied to his demonic contract. When he learns years later that Hyakkimaru survived and is traveling the land killing the very demons he made a pact with, Daigo views his own son not as family but as a direct threat to his life's work. He becomes determined to destroy Hyakkimaru to prevent the collapse of his domain and the exposure of his dark secret. This sets him on a collision course with his son, making him the story's principal human antagonist.

In the unfolding narrative, Daigo serves as the architect of Hyakkimaru’s suffering and the symbolic representation of human greed and callousness, which is often portrayed as being just as monstrous as the demons Hyakkimaru fights. His role deepens as he manipulates events and people around him to stop his son, including lying to Tahomaru to turn him against his own brother. This pits the two siblings against each other in a tragic conflict of Daigo’s own making.

Key relationships in Daigo’s life are largely defined by his ambition. With his wife, Nui No Kata, he is emotionally distant and dismissive, showing no concern for her grief over the loss of Hyakkimaru and only valuing her for producing an heir. His relationship with his heir, Tahomaru, is conditional, based on the young man's utility as a successor. While he shows more concern for Tahomaru than for Hyakkimaru, he ultimately manipulates him as a tool to eliminate the threat posed by his elder son. The most significant and antagonistic relationship is with Hyakkimaru, whom he rejects completely and attempts to have killed, viewing him as an abomination and a living threat to his domain.

Throughout the story, Daigo shows little to no traditional character development or redemption. He remains fixed on his goals, refusing to accept responsibility for the suffering he has caused. As Hyakkimaru kills more demons and Daigo’s lands begin to decay, returning to their former desolate state, he becomes more desperate and unhinged. Rather than repenting, he doubles down on his choices, even expressing regret that he did not personally ensure Hyakkimaru was killed as an infant. His development is a tragic descent where his ambition ultimately isolates him, leading to the destruction of his family and his domain.

As a notable ability, Daigo possesses no supernatural powers of his own. His strength lies in his political savvy, his skills as a strategist, and his authority as a feudal lord who commands a large army. He is a capable swordsman and military leader, able to lead his troops into battle. The prosperity and military might of his land are not the result of his own merit but are the direct consequence of his ill-fated pact with the demons. The only mark of his supernatural bargain is the X-shaped scar on his forehead, a physical sign of his contract with the forces of darkness.