Disclaimer: I know nothing about Dark Souls.
There's currently dark_souls tag for the first game, dark_souls_2 tag for the second, and dark_souls_3 for the third. There doesn't appear to be any tag that covers the whole franchise.
My proposal would be one of these:
- Create a dark_souls_(series) tag, implicate all tags to this.
- Use dark_souls as the tag covering the whole series, alias all tags to it.
Additionally!
The official titling seems to have numerals rather than numbers, so I also think that dark_souls_2 and dark_souls_3 should be aliased to dark_souls_ii and dark_souls_iii respectively.
Updated