Mansumi Oyamada is the father of Manta Oyamada, and he is the head of a big company.
Mansumi Oyamada is created by Hiroyuki Takei; he has no inspiration used to create him. He first appears in volume: chapter 47. He does not appear in the anime.
He appears in the hospital after Manta and Yoh were severely injured by Faust in the second Shaman King preliminary round. Mansumi informs Manta that he knows about Yoh's family and how shamans are a fraud; Mansumi tells Manta that he is going to school in America. When Manta refuses, Mansumi slaps his son. He leaves with his wife, his daughter, and their butler.
He has no powers, but he has the power of money to influence others.