Hanami
Hanami is the annual celebration of the cherry blossoms. Being a nature-oriented culture, Japan takes time out to observe seasonal occurrences, Spring being one of them. Hanami is not an officially sanctioned holiday but a culturally approved one. Because cherry trees bloom at different times of the year, students get the luxury of witnessing the first blossoms while office workers hope that the blossom stay long enough for the weekend.
Cherry blossoms don't last very long, a week and a half at the most. Therefore, it is Japanese tradition to observe hanami as a gesture appreciating the short span of life of the sakura (cherry blossom), and of human life.
How is hanami celebrated? Very simply. It is the one time out of the year when (except during baseball season) the Japanese can let go of their carefully composed behavior and let loose! Everyone has a picnic under the cherry trees, eating, drinking, laughing, moving from one picnic spot to the next where they visit old friends or make new ones. An American comparison might be the Fourth of July. Not that close, but its still a picnic or a barbecue, with some beer and sake, and beautiful flowers above you.
Hanami in Osaka and Kobe is supposed to begin the last weekend of March and runs through the first weekend of April. Tradition holds that the later hanami arrives, the shorter the summer. I certainly hope so.