SuperNova on 22 October 2016
It also has another 2,5m on Youtube japan and about 650k on the UK channel. It's not the most popular video on either of those (yet) though.
Does nintendo have an officil channel on that japanese video site that is way more popular than youtube over there?
(i forget the name).
Anyways initial response to the teaser seems to be positive and spread fast, hopefully this means the genral public will be more aware of the system than they have of the wiiU.
