Masashi Nishioka is a young editor who begins his career in the Dictionary Editorial Department at Genbu Publishing. He presents himself as a good looking and sociable man, with an easygoing and often frivolous demeanor. He possesses strong communication skills and a natural talent for navigating social situations, which makes him appear outwardly confident and well adjusted. However, beneath this surface, Nishioka harbors a deep insecurity about his own abilities. He views himself as an ordinary person without any specialized talent or consuming passion, especially when compared to the intense dedication shown by his colleague Mitsuya Majime. This feeling of being a plain individual in a workplace filled with fervent devotion to words becomes a central internal conflict for him.

Nishioka is initially indifferent to the work of compiling a dictionary, seeing it as a mundane task. His outlook changes when he meets Majime, a man whose obsessive love for language he finds strange at first. As they begin working together on the new dictionary called The Great Passage, Nishioka comes to recognize that their individual strengths complement each other perfectly. While Majime possesses an almost autistic focus on the nuances of language, Nishioka excels at the practical aspects of the job such as coordination, negotiation, and dealing with people inside and outside the company. This recognition sparks a significant shift in his motivation. He resolves that even if he cannot be a genius like Majime, he can dedicate his own talents to supporting the project from behind the scenes, choosing to value the substance of the work over personal recognition.

Nishioka plays a crucial role in the story by acting as a bridge between the isolated dictionary department and the rest of the publishing company. When the publication of The Great Passage is threatened with cancellation due to budget concerns, it is Nishioka who devises the strategy to create a fait accompli by rushing external orders, forcing management to continue the project. As a condition for continuing the dictionary work, he accepts a transfer to the Public Relations Department, sacrificing his place on the editorial team to protect Majime and the dictionary itself. Even after the transfer, he remains a steadfast supporter of The Great Passage, using his PR skills to handle its promotion and marketing. He becomes the chief of the PR Department later on, but he regularly returns to help the dictionary department, ensuring the project succeeds.

His key relationships are defined by this supportive role. He becomes best friends with Mitsuya Majime, and their friendship is built on mutual respect for what the other brings to their shared mission. He is also in a relationship with Remi Miyoshi, a colleague at Genbu Publishing, and he eventually proposes to her. His bond with the veteran editor Kohei Araki is professional and respectful, as Araki recognizes Nishioka's value even when Nishioka himself doubts it. Over the course of the story, Nishioka undergoes a clear development. He transforms from a cynical, somewhat lazy employee into a man who finds profound purpose in empowering others. His notable abilities are not related to linguistic expertise but rather to his social intelligence, his capacity for strategic thinking, his negotiating skills, and his adeptness at public relations and marketing. He learns to channel these abilities toward a cause larger than himself, finding pride in being the supporting pillar for the great work of others.