This study argues that trans-contextual migration experiences can lead to various changes in self-identification among multiethnic and multiracial Japanese individuals. This case study examines in-depth interviews with six participants with roots in Japan, Thailand, and Germany through a narrative-based approach. The author discusses the dynamic relationship between contextual and individual factors in influencing self-identification. Through thematic analysis of participant narratives, this exploratory case study identifies four recurring themes; migration can trigger significant changes in self-identification; migration can lead to unresolved mismatches between self-identification and societal categorisation; migration can result in the development of hybrid identifications that transcend rigid ethnic boundaries; and migration to a third cultural context can validate self-identifications in new ways. By examining themes that emerged from participant narratives, this case study illuminates the fluid and complex nature of multiethnic and multiracial self-identifications, particularly how racialisation processes intersect with ethnic identity formation across different national contexts. The study contributes to the growing scholarship on mixedness by emphasizing the importance of a biographical understanding of multiethnic and multiracial self-identifications through the lens of trans-contextual migration experiences.