This study aims to address the challenges faced by individuals with limb disabilities or single-hand users when operating computers, by designing a one-handed input device that integrates both keyboard and mouse functions. Through the use of a custom-designed PCB, personalized keycaps and switch layouts, a 3D-printed ergonomic casing, and the integration of a mouse sensor with QMK firmware, we developed a system that enables users to perform typing and cursor control simultaneously with a single hand. Experimental results show that, compared to conventional keyboard-and-mouse setups, the proposed device significantly reduces wrist movement distance and frequency during single-handed operation, effectively improving efficiency and reducing fatigue. The product design not only serves users with disabilities but also suits specific single-hand usage scenarios, demonstrating strong versatility and practical value. Future improvements in both hardware and software are planned to expand its accessibility and further realize the social value of assistive technology.