One-Way Flight and Exchange in Korea/Japan

Hi everyone.

I am a Singaporean student who will be on a student exchange in Sept-Dec in South Korea. I plan to go to Japan 2 times.
The first trip will be for about 3-4 weeks before i go to Korea.
The second trip will be for about 2 week after the Korea part of the trip.

I read the other forums posts and there seems to be quite a fear about one way tickets. Both my flights towards Japan are one-way.

My question is whether there is likely to be any problems with immigration, assuming I have proof of my flight out of Japan (ie, first trip I show evidence of my flight to South Korea and second trip I show evidence of my flight to Singapore)

Also, my friend has an exchange in Japan. Will immigration allow him to stay if he shows the Japanese student visa? Or does he need to produce like a open return ticket or something like that?

We are both Singaporeans.

Thank you very much for your replies.

If you have your ticket out of Japan when you enter, no problem, that's all they want to see.

Your friend can exit Japan and re-enter with the "special re-entry permit" system.

Actually it's not clear what your question is regarding your friend, please be clearer.

Hi, thank you for your reply.

Initially I was just wondering if my friend would have any trouble on his flight to japan. (My other friends all bought open tickets so that scared me a little) But I guess it should not be a problem?

He may be going to Korea as well. I checked up the special re-entry and it seems that no additional registration is required?

Source: http://www.immi-moj.go.jp/newimmiact_1/en/point_3-4.html

Is that correct?