This study explores new possibilities for transforming perceived space by using an umbrella as a dynamic spatial auditory interface. While spatial audio technologies have been widely applied across various domains, there are few opportunities in daily life to consciously perceive the boundary between personal and external space. Due to its physical structure and everyday usage, the umbrella has a unique ability to render such boundaries perceptible.Focusing on the "flow" of raindrops across the umbrella's surface, the system detects continuous rain movement in real time rather than merely capturing impact sounds. Spatial auditory feedback encourages users to actively perceive dynamic spatial boundaries, as the rain draws auditory contours through interaction with the umbrella.To this end, the umbrella is conceptualized as an interactive interface that senses raindrop movement and applies spatial audio processing. In addition, users can dynamically alter the virtual size of the umbrella, enabling perceptual shifts in spatial scale.Rather than treating the umbrella as a mere protective object, this system reimagines it as a medium for perceiving environmental change through sound. By integrating natural phenomena with spatial audio, this approach suggests new directions for embodied perception and expression.