Drawing on ethnic boundary-making literature, this study investigates how Korean newspapers and readers adjusted their ethnic boundaries towards Asian migrants in response to the evolving phases of the COVID-19 pandemic. We analyzed the extent and nature of coverage in five major newspapers on anti-Asian racism in the US published between January 1 and May 24, 2020, along with associated reader comments. During the maintenance phase, marked by persistent concerns about the resurgence of infections, we observed the highest number of articles and the most significant disparities between the media’s portrayal and reader reactions. Contrary to the newspapers, readers perceived the racist threat faced by Asian migrants differently depending on the pandemic circumstances, displaying a more flexible boundary-making. Despite the general description of Asian diasporas as “innocent comrades” in newspapers, readers viewed the Chinese and Korean diasporas as “blameworthy foreigners,” regarding them as potential threats to the nation. We discuss factors and conditions that might have influenced the formation of transborder ethnic boundaries among Korean newspapers and the public.