It’s not unprecedented for many games to simply skip out on releasing an Xbox version in Japan, even when an Xbox version for the rest of the world exists- Xbox does so poorly in the country that it makes not much sense to spend money releasing a version for the system. Notable titles, such as Final Fantasy 13, Persona 4 Arena Ultimax, and even Batman: Arkham Knight have all been among the ones that have foregone an Xbox release in Japan.
The next title to join that list may be Kingdom Hearts 3– people are noting that the title seems to have been removed from Microsoft Japan’s site entirely, indicating that the game may not get an Xbox One version in the island nation. Of course, this doesn’t have to mean much- for instance, Xbox One exclusive Scalebound does not yet appear to be on the Xbox Japan site either. However, given the prior history of games, and especially Square Enix games, opting to skip Xbox for their Japanese release, it’s not hard to see why people may jump to a conclusion like this.
Kingdom Hearts 3 will launch on PlayStation 4 and Xbox One worldwide, some time after March 2017. An exact release date has not yet been set for the game. It is set to be the conclusion to the story arc that began with the original Kingdom Hearts on PS2.