While the website is short on details, J-Startup is a#government program to give a "seal of approval" to#startup s. It signals to investors that the company has been examined already and appears to be a safe investment. There is no English information at this time but based on the Japanese sources I could find, this basically sums up the program.
Government press release:
Usage of the J-Startup logo (the "gold seal of approval")
Usage of the JETRO Global Acceleration Hub
A "Startup Tour" to various events in Japan, United States, etc.
This information isn't on the homepage.
The program is going to try to increase the length of a "Startup Visa"