This qualitative case study examines the language learning trajectory of a South Korean international undergraduate student (Stella) in the United Kingdom. Previous studies have reported a lack of research on the intricate relationships between motivation and investment. To fill this gap, this study examined Stella's shifting levels of motivation and investment according to her various identity negotiations by gathering data from multiple sources. This included interviews, reflection journals, and other written artifacts that were gathered over a year. The findings revealed that Stella encountered linguistically and racially marginalizing experiences due to her different accent and her Asian background. Because of her linguistic needs (e.g., higher second language [L2] proficiency, appropriate responses to injustice), Stella initially remained motivated to learn the target language. However, sociocultural challenges (e.g., identity-damaging experiences, and lowered self-efficacy) hindered her sustained L2 investment. These findings demonstrate that perceived positive attitudes from host communities are pivotal in enabling a virtuous circle of social interaction and long-term language investment.