In this work, we present a novel emotion assessment assistant based on respiration detection using a humidity sensor with high performance. The humidity sensor consists of a nanoforest-based capacitor to enhance sensitivity, a micro-heater to shorten response time, and a thermistor for temperature compensation. Such a sensitive humidity sensor can distinguish respiration states in different emotions. With an external stimulus for respiration regulation, an emotion assessment assistant is established. Such an assistant can distinguish emotions of different people, thus provides a visual way to monitor the emotional changes in real time. The assistant may have applications in smart mental healthcare in the future.