Tokisada Ryūga is the deceased patriarch of the Ryūga clan, a powerful family that controlled Japan's political and financial worlds from behind the scenes during the Showa era. He is the mastermind behind Ryūga Pharmaceuticals, the company responsible for the development of a mysterious and sinister blood-based drug known as "M". This drug, which granted temporary superhuman vitality, is implied to have contributed to Japan's war efforts and was the source of the family's immense wealth and influence. His death at the beginning of the story serves as the catalyst for the events that unfold in the remote village of Nagura, drawing both the salaryman Mizuki and Kitarō's father to the secluded community.

Despite being a seemingly passive figure who has passed away before the main narrative begins, Tokisada is revealed to be the story's true, overarching antagonist. His apparent death is a facade; his will, which is read to the gathered family, dictates a surprising line of succession. Instead of his capable son-in-law, Katsunori, the inheritance is left to his reclusive son, Tokimaro, and then to his young, sickly grandson, Tokiya. This calculated plan sets off a violent power struggle among the greedy relatives. However, the ultimate ambition behind this scheme is far more sinister. Tokisada refused to cede his power or wealth to any successor. He had secretly transformed himself into a malevolent spirit, allowing him to transcend death. He reveals his true nature by possessing the frail body of his own grandson, Tokiya, in a cold and calculated act that allows him to continue his existence as one of Japan's elite literally forever.

His motivations are rooted in a monstrous pride and a desire for absolute, eternal control. He does not see his family as heirs but as pawns. He allowed his daughter, Otome, to believe she was in control of the family's machinations, all while his spirit waited to reclaim his position. He views the Ghost Tribe, the race of yōkai to which Kitarō's parents belong, as mere livestock to be hunted and exploited for their blood to manufacture the M drug and fuel his ambitions. His ultimate goal is not just personal immortality but the continued prosperity of Japan as he defines it, a goal he believes justifies the horrific sacrifices of both humans and yōkai. His key relationships are therefore defined by manipulation and exploitation. He uses his daughter Otome as a surrogate to run his affairs, his son-in-law Katsunori as a disposable business front, and his grandson Tokiya as a vessel for his own resurrection. His primary opposition comes from Mizuki, whose humanity drives him to uncover the truth, and Kitarō's father, whose quest to find his missing wife leads him directly into conflict with the patriarch's atrocities.

Throughout the story, Tokisada does not develop or change; instead, his true, unchanging nature is gradually unveiled. He begins as a portrait and a contested inheritance, a symbol of power. He is then revealed as the orchestrator of the family's crimes, and finally, as a demonic entity. His development is a negative arc of revelation, exposing a human villain who has willingly shed his humanity to become a monster. In terms of abilities, as an evil spirit, Tokisada is capable of powerful demonic possession, seizing control of Tokiya's living body. He is also responsible for creating multiple Kyoukotsu, gigantic, grotesque yōkai fueled by the power of hatred, which he amasses from the countless corpses of his victims. He wields his family's wealth and influence as tools, believing himself to be untouchable and beyond the reach of mortality, ultimately serving as the physical and symbolic representation of the corrupt, postwar forces that Mizuki and Kitarō's father must fight.