Gunze market their own brand of softening and setting solutions, imaginitively entitled Mr Mak Softer, and Mr Mark Setter.
I have found these better able to deal with Japanese and Korean decals, as they are supposedly formulated for that very purpose.
They pull Tamiya decals down perfectly, though you have to be sparing with Hasa decals, which have a tendency to melt if you're not careful.
Karl