Otoya serves as Mao's steadfast assistant, and while he appears to be a quiet, unusually mature boy, he's actually a shikigami—a spirit bound into a physical object, in his case a small wooden doll shaped like a child.
His day-to-day work is straightforward: he carries Mao's tool bag, retrieves whatever the doctor needs, and helps however he can. He's patient explaining things to Nanoka, the time-displaced girl, though like Mao he finds her modern knowledge and behavior baffling.
One major advantage of being a wooden construct rather than human is that Otoya can withstand serious damage—getting sliced in half, for instance—and simply have Mao repair him afterward. More importantly, he's trusted with one of Mao's most critical possessions: the medicine jar that's the only thing keeping the doctor alive during severe injuries. When that jar inevitably gets destroyed, Otoya takes on the grueling responsibility of painstakingly reassembling a replacement and hunting down poisonous creatures to fill it.
Content compiled by AnimeList.moe from publicly available sources.
