Kōhei serves as a supporting character and a hospital colleague of nurse Mariko Hosoi. His professional role situates him firmly within the workplace setting central to the series. As a coworker, he interacts with the main character primarily in occupational contexts. His presence helps depict the protagonist's daily routine and non-romantic social interactions. Kōhei appears consistently across both seasons, fulfilling his established role within the hospital dynamic. His characterization remains focused solely on his professional capacity as part of the supporting cast, with no documented personal backstory, significant evolution, or narrative focus beyond this workplace function throughout all official installments.