In response to the need for more attention to teachers of writing (Lee, 2024), this collaborative autoethnography (CAE) aims to explore the lived experiences of Western-trained teachers teaching EFL writing in the tertiary-level educational context of Vietnam. Drawing upon the concepts of systemic tensions, emotion, and agency from an activity theoretical perspective, we report on tensions we encountered between our Western-based TESOL education and our local activity of teaching EFL writing as well as on how we emotionally and agentively responded to these tensions to allow for practices compatible with the local context. Our CAE unveiled a host of intricate tensions between multiple components of our activity systems. These tensions triggered our emotional responses, which in turn spurred us to exercise our pedagogical and relational agency to reconstruct our pedagogical cognition and implement adaptive pedagogies. Notably, the dynamic interplay between our tensions, emotion, agency constituted critical experiences which fostered the emergence of participatory pedagogical content knowledge of writing, and in turn, of situated possibilities for learning and teaching EFL writing. The study provides implications for Western-based TESOL teacher education and relevant stakeholders regarding how to better support teachers like us in our transition from learning in the West to teaching in the East.