Genres in ID3v2 tags are free-form Ascii text. So if you strip out your V1 tags and only use V2, you can put anything you want in there.

V1 tags have a hard-coded, standardized table of bytes-to-genres. However, there are two possible sets of tables, one which is 80 entries long, and one which is 125 entries long. The entire list can be found here. Note that "Anime" is not among that list. Anything beyond that list is nonstandard and can be expected to come up strange depending on which software you use.

When I use WinAmp to add "Anime" to a V1 tag, it comes up as byte value 145, which is way outside the standard range.