Oogami Masaomi is a seventeen-year-old Toushinshi, a contractor who summons and fights alongside shikigami spirits, in the anime. He presents an outgoing and sociable exterior, with a fondness for mopeds and donburi rice dishes, and he is often shown riding a motorcycle while buying and delivering boxed lunches to the young protagonist and his friends. He is introduced as a friendly and capable ally who repeatedly steps in to help when the main character is in danger, and he is the first experienced shikigami user to offer the protagonist genuine support and guidance.

Beneath this cheerful manner, Masaomi is a member of the Shinryuu school of Toushinshi, and like the protagonist he came from the past, having traveled to the modern era from the Heian period roughly a thousand years earlier. As part of the Shinryuu, he is involved in the group's covert efforts to revive Utsuho, a powerful being whose restoration threatens the world. His motivations are not purely villainous, however. He perceives that the protagonist is a lonely boy who has suffered the loss of his parents, and he deliberately exploits that loneliness in an attempt to make the boy stronger. When his manipulations drive the protagonist into a state of uncontrollable rage, Masaomi shows genuine remorse and apologizes, revealing a caring side behind his scheming.

Masaomi's contracted shikigami is the Azure Dragon Kibachiyo, a cheerful and lively spirit with whom he fights closely, and he is regarded as a powerful and knowledgeable user of shikigami. His closest ties among the Shinryuu are with Taizan and Onishiba, fellow Toushinshi who also came from the Heian period; the three are longtime comrades before their loyalties begin to diverge and they eventually come into opposition. Through his part in the resurrection of Utsuho and his shifting allegiances, Masaomi develops from a seemingly friendly helper with a hidden agenda into a figure caught between his commitment to the Shinryuu cause and his personal connection to the protagonist.