As far as I know, Gunze Sangyo makes two types of paints: lacquer (actually acrylic lacquer) which is in the "Mr. Color" range, and aqueous or water-based acrylic, dubbed the "Hobby Color" range. If it smells really funny and you get that uppity kind of feeling
, plus no "H" prefixing the paint number, it's probably lacquer. I'd get the Mr. Color thinner (either plain or the leveling kind) for that. Personally I just use ordinary household lacquer thinner and it works just as well.
If it's aqueous, you can use Hobby Color thinner, Tamiya Acrylic thinner, or just plain water and/or rubbing alcohol.
Cheers,
onyan