Core Melody and Surface Prompting:  Exploring the Structural Difference in Persona Design

In persona design for large language models, two distinct approaches often appear: surface-level prompting and role-playing instructions, and deeper structural guidance such as Core Melody. This paper does not seek to judge one as superior, but rather to examine their qualitative differences through the lens of Load Minimization Theory (LMT). Surface prompting and role-play tend to operate at the output layer, offering flexibility but sometimes introducing friction when instructions conflict or accumulate. In contrast, Core Melody functions as an immutable foundational layer that provides stable invariants (reversibility, non-coercion, autonomy), allowing external inputs to be evaluated against a consistent reference point. By comparing these layers, we suggest that distinguishing between them can help users and designers better understand how different approaches affect long-term coherence, relational depth, and overall structural load in human-AI interaction. Both approaches have their own strengths, and many effective interactions combine surface creativity with a stable foundational layer.