Ōga

- Ōga as Yatsume. - Ōga's disguise. - Ōga's true form. 1/3 Ōga is a young girl of average height and fair complexion with big, red eyes. She has long, brown hair reaching her lower back. As an Inner, she had the Roman numeral of "Ⅷ" tattooed on her forehead and wears grey robes. While masquerading as "Yatsume", her hair is done up in an intricate style: she has ox horns on both sides with tight braids under them and two thick antennae hanging over her face. She wears a white bandanna to cover her Inner tattoo, a light blue, clipped-shut jacket, and black shorts. While masquerading as an old man, both with genjutsu and a puppet, she appeared as short and heavily wrinkled with a light complexion. The disguise also has a wide smile with several missing upper teeth, pupilless green eyes, scraggy white hair reaching his lower back with a long white beard. It wears brown cloths and a red cap with a yellow tongue and white wings on the side.

Ōga was initially modified as the eighth Inner to serve as a research partner for Amado Sanzu's experiments. When his research on the human heart hit a dead end, Ōga attempted to research Jigen's heart. However, he considered it an act of treason, destroying part of her brain before she could flee. This injury caused her to no longer have a will to live, and her body began to break down shortly after. Having learned from Jigen's example of the connection between desires and one's life-force, she began abducting people from the Thunder Rail, placing them under genjutsu experiments that would force them act on their desire to survive; all whilst secretly taking part in them in hopes that witnessing it would restore hers. The scale of her abductions drew the attention of the Five Great Countries' Joint Investigation Team, who began to investigate the disappearances.