Don’t think it’s possible to sort the work permit until he’s played a certain percentage of minutes of a full season there. At least this means he’ll be a regular starter, and may force his way into the Japanese squad.
There are a couple of other criteria to be met, but yes, the decision on whether or not a pro sportsperson is sufficiently talented to have a positive effect on the standard of that sport in the U.K. is left up to the sport’s respective governing body.
I’m not sure that the easing of work-permit points requirements will make much difference to the big clubs. Most of the non-EU players that they signed in the past were established full internationals for sufficiently high ranking nations anyway. It probably benefits clubs like us that are...
Ultimately it’s the U.K. government. Although it’s up to the FA as the sport’s governing body to endorse the application as an elite level sportsperson. I guess they do this via the aforementioned points system.