Players who start the event will be able to pick up Yo-kai Medals from FATEs throughout La Noscea, Thanalan, and the Black Shroud. The medals can be traded in for various Yo-kai minions, and completing FATEs with those minions out will award players with Legendary Medallions which can be spent upon weapons. Players who earn all 13 minions will also be able to pick up the mount, while players who have all 13 weapons will… well, have a lot of Yo-kai weaponry. You’ll have two months to take care of all of it, so fans of the franchise or lovers of event rewards should jump in next Tuesday.
Source: Official Site