Tanabata originally came from a Chinese legend.
According to the story, the king of the heavens had a daughter named Orihime.
Orihime was a skilled weaver, and worked hard at her weaving everyday.
But because she was always working, she would never fall in love.
Her father saw this and feeling sorry for her, introduced his daughter to Hikoboshi, the cowherd.
The two got married, and were so happy together that Orihime stopped weaving and Hikoboshi stopped caring for the herds.
The king of the heavens was furious and separated them across the Milky Way.
But when he saw his daughter sobbing, he agreed to allow them to meet once a year, on Tanabata, July 7th.