This article investigates how Japanese university students perceive Japan's domestic diversity and understand the role of English within that context. Surveys and interviews with Japanese students reveal how they reflect on their own experiences with diversity in their past English as a Foreign Language (EFL) classes and also help to explore the role of English teaching/learning in multicultural Japan. Insufficient attention to domestic diversity may mislead EFL learners when they encounter their English interlocutors with different cultural and linguistic backgrounds because this misunderstanding can create prejudices about English speakers and may reproduce a racial/ethnic and linguistic hierarchy. Drawing on the survey and interview results, this article suggests possible strategies for promoting successful intercultural communication through English and teaching English as a global language.