The Hakurei Shrine Reitaisai (博麗神社例大祭) is an annual convention held in Japan to officially release demo and full versions of Touhou games. Fan works are also released at the event.
Reitaisai 8 was originally scheduled to be held in Tokyo Big Sight (Tokyo International Exhibition Center) on March 13, 2011, but was postponed to May 8 after a major earthquake on March 11.

Official website: http://www.reitaisai.com/