No matter how much you prepare or what resources you use, you will never be ready for the real thing until you actually get used to the real thing. Whether that may be books, conversations or like in your case JRPGs. It’s not like you’re just gonna study something and then you’ll have no problems consuming whatever media you like. The ease will only come with time and experience
I myself didn’t specifically study for any games, but I have finished a few Japanese games, the longest of them being Persona 5 Royal which took me about 130 hours (it’s a really long game). While I haven’t tried any Final Fantasy games in Japanese and thus can’t really judge the language difficulty, I can recommend Dragon Quest games as your first step into playing JRPGs in Japanese. These games have a wide target audience, including children, and so they’re relatively easy to understand compared to some other RPGs that are out there. The latest main entry in the series, Dragon Quest XI (S), also has a huge demo available that encompasses the first ten or so hours of the game with the ability to import the save file to the full game if you decide to purchase that, so that’s something I’d always recommend. Depending on your platform, you might have to set the region of your account / PC / console to Japan first to get the Japanese version of it
In short: I don’t think you’ll be prepared by studying specific things beforehand, but rather that a gradual progression from easier to harder (in terms of language) titles might be best
One thing to keep in mind is that if you pick up any type of media, video games or otherwise, they are going to have a ton of words that only appear once or twice.
There’s quite a bit of overlap between that list and Wanikani for the top few hundred that I scrolled through.
An idea is commonly used words aren’t enough. Unless the word list is manually made, it depends on how frequently list is made (segmentation). Words aren’t necessarily enough to understand compound words, nor phrases. It also depends on context. And another thing is yeah, sources just vary.
WaniKani has a differently idea (although it does have some compromise to the idea above). Instead of studying by frequency (of a Kanji), we study by Kanji complexity (and building up of radicals) instead.
It is true as well, that is possible to infer meaning (and reading) of compound Kanji words, by Kanji; especially if such words are relatively rare. Otherwise, it wouldn’t be hard to look up on time
It’s totally possible to study vocabularies you’ve found yourself, by relying more on Kanji building up, rather than frequency. WaniKani is quite an established by method, so maybe something that applies the idea? I am doing this in Anki. Not sure if WaniKani Custom works well - haven’t tried myself. There may be simpler methods I haven’t realized yet.
