In spatial UI systems used in VR and AR, hardware interfaces are widely employed as metaphors. Utilizing metaphors offers advantages such as facilitating the construction of appropriate mental models for behavior and enabling accurate operations. However, in existing spatial UI metaphors, operability is often sacrificed. In this research, we propose Bubble-UI, which utilizes soap bubbles as a UI metaphor, aiming to enhance comprehensibility and improve performance by leveraging interaction knowledge. As applications, we propose three types: "Bubble-Button" for button operations, "Bubble-Holder" for object manipulation, and "Bubble-Loading" for loading representations. Among these, experimental results for Bubble-Button indicate that it is faster in input speed, less tiring, and more attractive compared to other methods, while exhibiting a higher error rate.