Wikibooks does not have a user page with this exact name. In general, this page should be created and edited by User:欣之介くん. If in doubt, please verify that "欣之介くん" exists.
If a page was recently created here, it may not yet be visible because of a delay in updating the database; wait a few minutes and try the purge function.
Titles on Wikibooks are case sensitive except for the first character; please check alternative capitalizations and consider adding a redirect here to the correct title.