score:4
(Qualifier: I live in Japan )
This is common. Just ask at immigration for a regular visitor visa, explain that you want to use the WH later. Maybe put a post-it note over the WH visa and write γΎγ on it (means "not yet").
Upvote:1
I know a number of people have accomplished this by flying to nearby Seoul between when their tourist visa ends and their work visa begins. Fly there a couple of days before your work visa begins, have a short stay there, and then arrange your dates so that you re-enter Japan when your work visa is valid.
Not sure if this is a reasonable option for you, but it is a guaranteed way of doing this.
(I have lived in Japan working for 8 years)