The rapid development of technology has greatly contributed to the innovation and popularization of smart wearables, which has not only made significant breakthroughs in functionality, design aesthetics, and user experience but also pushed forward the advancement of related technologies. However, existing research has found that one of the main limitations of current smart wearable devices lies in the limited nature of the interaction interface - especially the limitations of the screen size and the singularity of the input function. Skin is a permanent, portable, and flexible natural interaction interface that can be used as a novel interaction carrier. In this study, an innovative on-skin input and output system is proposed based on the exploration of skin properties and improved sensing techniques. It is designed to use human skin as a virtual interaction medium, allowing users to issue various operation commands by executing different interaction gestures on the arm skin to realize different functional applications; in addition, feedback information is provided intuitively and dynamically by projecting a virtual interface on the skin on both sides of the arm and the back of the hand as the visual output of a dual-screen display. The main contribution of this study lies in its exploration of future interfaces, especially the potential of using skin as an interface to realize physical and virtual interactions. This not only provides a theoretical basis for understanding new dimensions of human-computer interaction but also opens up an under-explored interaction space, bringing new design ideas and possibilities to the smart application market.