Sickly Days and Summer Traces documents the relationship between a devoted brother and his sister over the course of a single summer. The two live together in a remote country estate, a setting designed to help the girl recover from her poor health. As her constant companion, the player-controlled protagonist takes part in daily activities, chronicling their time together in the countryside. These shared moments include collecting morning dew, watching the clouds, and whispering under the stars at night. The story explores the care and closeness that allows for the development of an exceptional and unwavering love between siblings.