This study takes a dynamic view of transfer as reusing and reshaping previous knowledge in new writing contexts to investigate how novice Japanese as a foreign language (JFL) writers draw on knowledge across languages to construct L1 and L2 texts. We analyzed L1 English and L2 Japanese argumentation essays by the same JFL writers (N = 19) and L1 Japanese essays by Japanese university students (N = 21), along with JFL writers' reported reflections. The analysis identified both shared and contrasting L1/L2 text features, including argumentation subtypes (e.g., "justification", "exploration") and essay introduction/conclusion components. The findings revealed that while constructing L2 essays, the JFL writers took an active role in assessing audience, selecting appropriate text features, and transforming/reshaping selected features, influenced by contextual factors (e.g., audience expectation, purpose, topic). For example, some writers reshaped their L1 "justification" subtype by softening L2 assertions to meet perceived Japanese reader expectations. Results highlight the centrality of the writer's agency in deciding what previous writing knowledge to reuse or reshape when creating L2 text and also the importance of individual learning trajectories (e.g., L2 proficiency, L1/L2 writing experience) affecting writers' decisions. The study affirms that a dynamic view of transfer provides insights into the L2 writers' text construction process.