In spring, they sowed seeds.
In summer, they irrigated the fields.
In autumn, they harvested the fruits.
In winter, they sang as they walked in the snow.
...
The land that was originally barren now blooms with flowers, and butterflies are drawn by the peals of laughter and land on the girls' fingertips.
"Big sis! We'll keep working together to turn this into a huge sea of flowers!"
"See. Our promise..."
The butterfly flies to the other shore. The rather taciturn girl softly caresses the warm flower petals as if her little sister is still there with her.
"...Wasn't forgotten by me or the flowers we once attended."