Adashino-sensei is a recurring character who serves as a doctor in a coastal village, though his primary passion lies in the study and collection of objects related to mushi. He is a tall man with pale skin, short, spiky black hair, and dark eyes, and he is almost always seen wearing a dark yukata along with a monocle over one eye. This visual detail of the monocle, which reflects light, is often symbolically contrasted with Ginko’s covered eye, which represents darkness, highlighting their complementary natures.

In terms of personality, Adashino is defined by a deep and somewhat obsessive curiosity about the physical remnants of mushi. Unlike the wandering Ginko, who maintains a minimalist and detached lifestyle, Adashino is settled and driven by a desire to possess and catalogue mushi-related artifacts. He maintains a shed behind his house where he stores his growing collection, which he acquires from various sources, including Ginko. His eagerness to obtain these items, even those that are potentially dangerous or of questionable authenticity, reveals an excitable and acquisitive nature that stands in stark contrast to Ginko’s more cautious and philosophical approach to the spirit-like creatures.

Despite their differing worldviews, Adashino and Ginko share a long-standing and mutually accepting friendship. Their relationship is built on a foundation of respect for their individual perspectives. While Adashino focuses on material accumulation and Ginko on transient solutions, they understand each other's methods. This is evident in moments where Adashino acknowledges that becoming one with a mushi could, for some people, represent a form of happiness, a sentiment that aligns with Ginko’s respect for personal choice in dealing with mushi afflictions. Their interactions often involve Ginko bringing unusual objects for Adashino to examine or purchase, providing a regular point of connection between the itinerant mushishi and the settled collector. In this dynamic, Adashino functions as a kind of stationary authority and mentor figure, offering a contrasting methodology to Ginko's wandering lifestyle while also providing him with resources and information.

Adashino’s role in the narrative is primarily that of a confidant and a foil to the protagonist. He appears periodically to provide Ginko with a place to rest, to discuss particularly enigmatic mushi cases, and to help with research, such as when the two used old maps to track the path of a traveling swamp. While he is not typically involved in the direct resolution of mushi-related incidents in the field, his knowledge and collection are valuable assets. In one extra story set years after the main events, Adashino is shown still assisting people affected by mushi, demonstrating that his obsession has not waned. However, in a moment of reflection, he comes to accept that mushi are not everything, sharing a quiet, contemplative moment with Ginko as they watch a sunset, indicating a subtle development in his character toward a more balanced perspective. Beyond his medical practice, his notable ability lies in his extensive scholarly knowledge of mushi and his keen eye for identifying and preserving artifacts related to them.