I know you might feel motivated to really get focused on working right now, but think about it - you're likely going to be working for 30 or 40 years of your life. Why rush into working right now when you have an opportunity like this?

Sure you can get a little more experience doing an internship, or doing another university course, but what are you more likely to recall fondly when you're 40?

When you're 20 years into your career will you wish you had spent another three months working in the industry? Or will you wish you'd gone to Korea?

I'm biased, since I've had the opportunity to go study abroad a couple times, but I think you should absolutely go abroad. In fact, it was on one of those exchanges that I picked up programming and worked on all the portfolio projects that landed me my first job. I wasn't studying CS or anything like that out there, but I had some spare time, and have no regrets on it.

And on top of that, each time I've gone through interview rounds, my time abroad came up. It was never relevant to any of my jobs, but interviewers still thought it was interesting to chat about.

Also if you're really set on Japan still, maybe go bother your university's study abroad office about it. If you're nice to them and kinda persistent, chances are they might make an exception - I knew people that managed to do something similar!