This event is planned to happen on Sunday at Yoyogi Park Event Area:
But I have heard that part of Yoyogi Park is closed due to a dengue fever outbreak:
The Japan Times
Will the event be held?
Cancellation of the event was announced on September 5.
As of September 4, the event will be held according to this document on the festival's website:
Note: Their website has invalid SSL certificate.
It says the event is held but they will have anti-mosquito coils around, and people should wear long sleeves.