This study examines the dynamics of diversity management in a contemporary workplace by focusing on how a company attempts to pursue "authenticity" in the process of overseas expansion and the challenges it may face during the process. Managing employees with different ethnicities and cultural backgrounds has been regarded as one of the most challenging issues for many Japanese companies overseas. This research explores this issue based on a case study of a Japanese ramen company, hereafter referred to as "Yama Ramen" in Boston, United States, and analyzes how the company attempts to create an "authentic" Japanese brand by representing its "Japaneseness" in management while struggling to adapt to the local context. The fieldwork, including participant observation at the shop and interviews with the employees, was conducted in March and May 2017 in Boston. Through the discussion, this study posits that at Yama Ramen, pursuing "authenticity" is a way to promote its brand but is also a process of negotiating the meaning of "Japaneseness." During this process, many Japanese managers have cultivated an ethnocentric ideology, which has become stronger alongside their interactions with the locals. This belief discouraged the Japanese managers from learning actively from the locals, but tried to convince them that the Japanese way was the best, which resulted in creating unharmonious human relations. This study highlights the negative aspects of implementing an ethnocentric ideology in a business context and the possible results of neglecting a respect for diversity. Its conclusion offers a few recommendations to the company for future management practices.