Transfer of funds between Shinsei and Deutsche Bank (Germany) has always been a matter of two to three days for me - in both directions.

Shinsei also has the link with Yucho (Post Office Bank), which means you can use all their ATMs - on top off all thousands of 7Eleven ATMs, and just about any other ATM.

But as I said, for OP doing without a Japanese bank account for a few months would probably be the least hassle.

As far as I know, Yucho wants to be a normal bank now and they are discussing integrating their systems into the IT link of the main Japanese banks, which should help with transfers and the like in the future.