Capitalization for unique title and quotations trickiness in inner thought

So, I have been writing and wonder whether to capitalize the word "master."
No rush here, I know that without name the word like this won’t be capitalized. But if it use as a substitute for one’s name and it being a title of something like "Dungeon Master" then it should be capitalize, right?
I’ve been checking a few novels that used these words but they tend to capitalize them, however, quite a lot did the otherwise.

Also, I’m a bit confuse whether to capitalize the word "world’s will" in this context:
The world’s will? Is she telling me the truth? But I remember reading about the theory of Gaia.

A second problem I found was about emphasizing a thought.
For example:
She’s older than me despite how she looks, but she still calls me ‘uncle’ and still call this stand owner ‘mister’…
She’s older than me despite how she looks, but she still calls me "uncle" and still call this stand owner "mister"…
I know for sure that single quotation mark only used inside a dialogue that already has a double quotation mark in use. But inner thought on the other hand didn’t use the double quotation mark and just plainly used italic. Is this just a style choice or there is something deeper?

Any help, please? Thanks in advance.