The most beautiful time to be in Japan is right now -- cherry blossom season. Oha-nami cherry-blossom-viewing parties are taking place everywhere, and you don't need an invitation to go to one.
As a matter of fact, almost anything you do, as long as it is under a cherry tree, is considered ohanami, (flower-watching).
Stroll along a cherry tree-lined road, and you can say you have done ohanami.