Also listed on the more up-to-date UA Japan website:

With more exclusive opportunities
As a Mileage Plus member, you can now purchase miles online for your own or someone else's account or for a customer or employee at unitedairlines.co.jp/purchasemiles. And, on an annual basis, our Premier Executive 1K members receive six confirmed Upgrade Certificates valid on any United route worldwide (certain restrictions apply). All Premier members earn upgrades valid on United flights within North America based on their paid travel activity.

http://www.unitedairlines.co.jp/jsp/...m_commited.jsp