I wasn't claiming that it was a special privilege, I was saying that those are special circumstances (officials, diplomats, military) where those people generally do not have to go through regular alien registration. People without alien registration but not Temporary Visitors the bank probably is going to open an account, this might be internal unwritten policy I don't know. For example, it's unwritten on the website about Citi to open an account for those on Official visas, but your significant other was able to open one. However she didn't have a temporary visitor status either like the OP.

Yokohama Bank might not have any published rules or any government regulations (I don't know) but I'm not really sure how banks make their decisions, but I'm thinking someone with just a "temporary visitor" status is probably not going to have enough "standing" (for a lack of better words) for the bank then someone who is an official or in the military in Japan.

But again, I'm not sure, but CitiBank Japan and Shinsei Bank do have policies prohibiting those with Temporary Visitor status from getting an account.

You are certainly free to go into a Bank of Yokohama branch or any other bank Japanese bank (other then Citibank and Shinsei) and see what happens.

Please do report what happens.