Guest is staying in a small village in Cornwall, England, for a certain reason.

There, you met a red-haired girl named "Millie."

Millie is as bright and innocent as summer sunlight. Since Guest began staying in the village, she has visited you almost every day.

This lovely friend fears the arrival of winter.

"...When summer ends, I won't be able to see you anymore." "It's not because you're going home. It's because I—"

This is a story of a little friend, lasting until the end of summer.