This study introduces a novel adjustable fastening mechanism for wearable robots, aimed at alleviating user discomfort associated with traditional fixed attachment methods. By utilizing the unique scissoring effect of braided sleeves, we demonstrated that axial manipulation can effectively translate into radial size control, allowing for precise regulation of fastening force. To address the size limitations of commercial braided sleeves, we developed a large-area fastening structure by combining multiple braided sleeve sheets. Additionally, we incorporated a wire tendon system to enable active operation in both Daily Mode (fastening-release) and Exercise Mode (fastening-tightening). Experimental results on an anthropomorphic model revealed that this adjustable fastening structure offers variable fastening forces, achieving a 4.8-fold difference between the exercise and daily modes. This research presents a new approach by leveraging the Poisson's ratio properties of braided sleeves for dynamic fastening, tackling fabrication challenges for large-area structures, and improving user comfort and compliance in wearable robot applications