The COVID-19 pandemic has negatively impacted the mental health of healthcare workers in many countries including Japan. While many survey-based findings have reported the serious state of their wellbeing among healthcare workers, the first-hand experience of the mental health and coping in this population remains to be evaluated. Accordingly, this study aimed to appraise them using constructionist thematic analysis on semi-structured interviews attended by a purposive and snowball sample of 24 healthcare workers in Japan conducted in December 2020–January 2021. Four themes were identified: (1) increased stress and loneliness, (2) reduced coping strategies, (3) communication and acknowledgement as a mental health resource, and (4) understanding of self-care. Participants noted that the characteristics of Japanese work culture such as long hours, collectivism and hatarakigai (i.e., meaning in work) to explain these themes. These findings suggest that robust support at an organizational and individual level, capturing intrinsic values, are particularly important for this key workforce to cope with increased stress and loneliness, leading to better patient care.