Seasons
A grain's child will grow with the seasons. In spring the grain is born, it grows in summer, is harvested in fall, and dies in winter.
Watch the grain children live their entire lives throughout the seasons. Though there are 72 seasons in Japan, so the life of a grain is actually really long there.
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All of the seasons have their own special key (き). As they change, that season's key appears and unlocks the next step in the grain's life.
Picture these seasonal keys floating through the sky, unlocking the weather changes, the growth of new grains, and the aging of us all.