As far as I can see, everything looks OK.
I guess "Iroha Kami" is the right material?
Ther seems to be noo issues with that single sided shader, nor with a black base color or "metallic" is tuned in.
Nevertheless, the texture is showing up correctly in Unity.
Are you sure you don't have any light sources in your unity scene, so that the asset has a dark lighting?
Don't seems so.
Strange thing is, that in VaM there seems to be a texture as well.
If not, it would be most likely white according to the material settings.
Two things...
First: are there any error messages or warning signs when exporting as unity asset? Is there something wrong with the texture?
Second: I guess, you maybe have created a black haired asset first...?
Did you have deleted the old file in the asset creating window (sorry, I am at work and can't take a look how it was s named correctly), and have dropped in the newly saved one?
Do they have the name? Maybe try to save the scene again with an other name, clear the asset creation thingy from any old files and drop in the new one.
(Third... did you really have copied and renamed the newly created asset in the VaM folder? Sometimes I forget to rename the asset file and then I only see an old version).
((Forth: Do you maybe have issues with the VaM texture cache? Please look after the cache settings, are there error messages? Did you already tried to restard or hard reset VaM after creating the asset?))
