Tanabata is the night of July 7th, when Orihime and Hikoboshi cross the Milky Way to meet once a year. We celebrate this night by writing our wishes on paper slips and hanging them on ornamented bamboo as a prayer.
The Tanabata legend goes like this:
Orihime, the daughter of the Heavenly God, was a diligent worker skilled at weaving, and she met a diligent cowherd named Hikoboshi. They fell in love with each other at first sight. They got married, but they neglected their duties and spent all their time together. The Heavenly God got angry with them and separated them, placing each of them on opposite sides of the river. As Orihime was so depressed and cried, the god allowed them to meet on the night of July 7th, but only once a year.