I have a japanese wii but I am not too sure on what I need to get it playing backup copies. Can anyone help?
I believe I need a step down transformer which allows it play on UK 240v. Then which modchip can be installed on a japanese wii to play backups?
Modchips are not based on region. Take a look at the following thread.
You'd have to open it up and find out which drive chip is in it. I don't think there were any extensive serial number tables for drive mods for Japanese region units (probably all on Japanese websites ;p).
Once you open it, you can decide which chip you need.