Sorry, I am a bit late with this one. Tanabata (Star Festival) is celebrated July 7th - August in some places.
Tanabata originated more than 2,000 years ago with an old Chinese tale called Kikkoden.
Once there was a weaver princess named Orihime and a cow herder prince named Hikoboshi living in space. After they got together, they were playing all the time and forgot their jobs. The king was angry at them and separated them on opposite sides of the Amanogawa River (Milky Way). The king allowed them to meet only once a year on July 7th. This is why tanabata is also called the Star Festival. People say that Orihime and Hikoboshi can't meet each other if July 7th is rainy, so they pray for good weather and also make wishes for themselves.
People write their wishes on tanzaku papers (colorful, small strips of papers) and hang them on bamboo branches. People also hang many kinds of paper decorations on bamboo branches and place them outside their houses. Many cities and towns hold tanabata festivals and have tanabata displays, decorating the main streets. In some regions, people light lanterns and float them on the river, or float bamboo leaves on the river.
Sendai City has a very famous Tanabata festival.
BabyEbi (with my help!) wrote his and hung it on the bamboo decoration at the shien centre.