This case study examines the key steps and challenges that were involved in a mixed methods research project relating to Japanese first-year medical students' English academic vocabulary learning. Conducting mixed methods research can be both conceptually and administratively challenging under any circumstances. However, this study was especially challenging given that it was undertaken during the COVID-19 pandemic, which necessitated hybrid data collection (via internet-mediated and in-person methods) of both quantitative and qualitative data. This paper primarily involves researchers' reflections on a number of aspects of the planning and execution of our mixed methods research project. Particular attention in this regard is devoted to (1) the steps that the researchers took to ensure that we were able to attain (and retain) a sufficient number of participants in our project, (2) how we designed and adjusted our research instruments to obtain valid data, and (3) how we managed the quantitative and qualitative data collection process as a whole. In doing so, we aim to provide researchers with insight into not only the importance of careful planning of mixed methods research but also the need for flexibility to be built into such planning in order to deal with issues that arise during the data collection process. Finally, this paper will also demonstrate how maintaining open communication with fellow researchers and participants can be a crucial determinant in the success of such a multifaceted mixed methods research project. [This content is provided in the format of an e-book.]