[Object] To provide a communication system and a storage medium that are capable of transmitting physical expression information of a user via a versatile communication application.[Solution] The communication system includes: a control unit configured to execute a communication application for directly or indirectly transmitting and receiving text information to and from a communication destination; and a communication unit configured to directly or indirectly transmit text information acquired via the communication application, to a communication destination. The control unit activates a utility in response to a request from the communication application. The utility acquires sensor data detected by a sensor, extracts specific expression information from the sensor data, converts the specific expression information into text information, and outputs the text information to the communication application.