How acceptable is it to take an unpaid leave?

For context, I’ve been working for a Japanese company for almost 2 years now. I got 11 paid leaves for this year. (So few in number I could cry)

I currently have 5 paid leaves remaining, to go back home. My flights are booked and my leaves have been approved by my boss.

However, I wanted to take one more day off, combine it with a three day weekend, that’s on my company calendar & go visit Okinawa.
Is it acceptable to request for 1 unpaid leave?
Is this looked down upon in a Japanese company? How do I ask my boss? Should I just tell him the truth – that I want to visit Okinawa. I’ve never taken an unpaid leave before.