When she was five years old, the heroine and her twin sister entered a huge forest and got lost. While searching for her sister, she met a boy of similar age to herself...
After walking out of the forest with her sister, the heroine discovered that her parents who were supposed to be waiting outside the forest disappeared. After returning home, they found a note left by their parents, to the effect that they were told to fend for themselves and would return to them at some point.
As a result, the two sisters grew up dependent on each other with the help of relatives...
When the heroine was fifteen years old, she met a boy who was suspected to be the boy in the forest, and unexpectedly received another interpretation of the note and other clues left by her parents. The story begins here...