The rapid and widespread deployment of Internet of Things (IoT) sensors is limited by issues related to maintenance costs and safe battery disposal. While battery-less systems supported by harvesting ambient energy offer a potential solution, the weakness and instability of ambient energy result in intermittent execution. To provide data consistency, I/O operations are usually performed in the atomic sections, resulting in low-energy efficiency and low-system progress in intermittent systems. To improve application responsiveness and prevent low-energy efficiency due to atomic I/O operations, we propose a framework named FASE, which provides energy isolation assistance to support multiple asynchronous atomic I/O operations in intermittent systems. Our proposal was evaluated on a real platform, and the results show that, compared to state-of-the-art works, our proposed algorithm can increase the rate of completion for latency-sensitive applications by more than 50%.