I think that slots with Japanese characters or manga will not be famous outside of Japan because these characters are familiar to a very narrow circle of people. In my opinion, to increase interest in slots, you should use more well-known characters or use a neutral theme that suits anyone regardless of where they live, interests, age, etc.
There are millions of anime fans all over the world. I do not think that the fanbase are too narrow or just a small circle for this theme.
Just look at this statistics and see it yourself how huge the audience of anime is. So I think it is not a waste to have an anime themed slots.

Take note China is not included there since Chinese government puts up strict regulations on anime and I am sure there are lots of Chinese anime lover.
I bet at least a couple hundred millions of young people in China love anime and watch it.

I don't know how accurate Google is in this particular case, but it's pretty accurate normally.
So, I think by number of people watching anime China would take the first place. What's interesting is that from the table you quoted, USA is number one in this regard. That means that the slots from the OP can be even only US oriented and still make good money.