Pre paid visa/mastercard for japan/HK region?

I dunno, I've left a map. It's basically get to Akihabara electric town exit, as you exit the gates, turn left, walk to end of road, turn right, walk to end of road, Cross the big road, walk straight keeping on the main road until you get to the lights, turn left, cross road, cross over bridge over river, walk straight, see post office. Seriously I found these in my first week of being here back in 2004, just a case of using a map...

 

Based on your instructions, I would far rather hit a Citibank somewhat close to a station and not have to bother.