Takeshi is Takeru Oyama's father, as well as the guardian of Inaho. Takeru was on bad terms with him after his mother died, running away from home and going to into a rage upon learning that it was him that sent Inaho to Tenbi.
Takeshi is extremely powerful, and was a teacher at Tenbi Academy while Minori and her classmates were students. It is possible he was the Maken-Ki supervisor, as Minori has a photo with the Maken-Ki group and Takeshi together. He is currently the master of the Oyama dojo, and one of the few instructors who can use and teach casts.