So this video explains that Yo-kai Watch Blasters has a problem that prevents 100% completion.
In the Japanese version, the game could connect to an Arcade version of Yo-kai Watch Blasters that provided items. Of course localizing the Arcade game would be unfeasible, so surely there would be an alternative to getting the bonuses right? Nope. By removing the feature, they prevented players from getting these bonus items. Items that are required for creating powerful weapons, and by extension getting an in-game achievement for getting every weapon.
This seems like a stupid oversight that really should be fixed with a patch.
I get it Level-5, Yo-kai Watch isn't a super-high priority in the West now, but don't hang us out to dry like this like you did with the Psychic Specters glitches.