This paper presents an exploratory case study of the classroom motivational dynamics of an English as a foreign language (EFL) teacher at a Japanese technology college. The article examines how motivation evolved in-context over various timescales through interactions with affect and identity. An introspective research journal generated rich, qualitative data concerning fluctuations in teacher motivation over one academic year. The analysis also drew on student journal data to provide a different perspective on teacher reflections. The study applied a thematic analysis, with "theoretical comparison" (Corbin & Strauss, 2008) to understand teacher motivation from a "person-in-context relational view" (Ushioda, 2009). The article utilises the properties of complex systems to render insight to the evolution of teacher motivation as open to influences "external" to the classroom, yet fundamentally tied to adaptive experiences with a particular class group. A variety of diagrammatic tools are also employed to illuminate the relational development of teacher motivation, affect and identity constantly occurring over interacting timescales.