War on Basics

You need to learn at least some basics first. Along with RTK (talked about in the next segment), avoiding learning any grammar is one the biggest moronisms of AJATT. So you’re gonna legit push for starting immersion without even knowing what です and -ます mean, or how particles are used? Oh, you say it’s not important in the long run anyway?
Shut up. Go to your room. I seem to remember there being something about comprehendible input in the “science department” of AJATT… Must be imagining things. Clearly if comprehension was the core of your method you would’ve advised people to at first get at least some sort of familiarity with how the language works, so that they could stand at least some kind of chance comprehending at least something in their immersion. As opposed to, I dunno know, literally nothing? Yeah, so much comprehension. Very input. Getting smarter every minute, no doubt.
That is yet another display of lacking self-awareness that almost every AJATT guru shares: they completely ignore the fact that they themselves had actually been with the language for quite some time before they went full immersion after giving up on other study methods. Meaning: they were very familiar with the basics by the time they moved to immersion and were able to comprehend random bits and pieces. They themselves didn’t actually do the “no grammar cold start”… But they would like you to do it. Because…? Well, that’s what selling language courses on redtube is all about, I suppose: you just come up with things that you’d like to be true and then push them as truth. You see, when you know everything you don’t really require any kind of evidence for you theories: they just automatically become reality… as long as you don’t leave your discord server.

Japanese from Zero, book 1 is by far the best place to start. That book is an absolute, one-of-a-kind masterpiece. Written by a mad lad polyglot truly in love with helping people get good. If you absolutely cannot wait to get into immersion, feel free to stop at book 1, but I recommend going through at least book 2 as well before doing anything else (even though it is not as insanely good and useful as the first one). After book 2 JFZ starts becoming progressively less mind-blowingly useful, but I wouldn’t say there is absolutely no value in books 3 and even 4. Book 5, however, is where I draw the line: by book 5 all the basic grammar is covered, but the remainder of the advanced-ish grammar in the language is so vast that one book could only cover maybe like 5% of it. So, the book covers pretty much nothing of what you want to know at that point: just a few random things. Whether you read it or not doesn’t make any difference, really. IMHO book 5 should’ve just been about how to study further by yourself (kind of what this website is).

I also recommend learning hiragana and katakana (along with some very basic vocab) like a normal human being in a few days instead of following the “progressive” system of the first two JFZ books: a very questionable invention of the author, to be honest. Although, in his defense: the book was written for all possible Japanese learners and not just for geniuses like you and I. Some of those learners include people who just want to study as much basic grammar as fast as possible so that they could be じょうず’ed by their way out-of-their-league crushes Japanese classmates. So give the author some break, mmkay? Without the progressive system… It would take some people maybe even a whole week (!!!) to learn kana — they need the ability to learn grammar and vocab NOW, goddammit! JFZ hears. JFZ provides. I don’t blame. Much.
I should mention that the author has quite a few other inventions as well: I find all of them rather brilliant, and fully support his “unorthodox” (i.e. correct) approach to defining and explaining a lot of grammar (something that by the “official” mainstream linguistics is fucked up beyond belief).

If you want to continue learning grammar points after JFZ book 2, along (or instead of) books 3 and 4 I suggest you get some of the TRY! books. Trust me, I’ve seen a lot of Japanese grammar books, and most of them are absolute trash. The TRY! series is not only not half bad — it is actually pretty OK. Alternatively, especially if you are on a limited budget, you can just start parsing the japanesetest4you.com website. JFZ is still my “№1 place to start before you do anything else” recommendation though. The problem with relying on textbooks after covering the basics is that there is only so many grammar concepts that can be explained to you before they become mere drops in the ocean. Diminishing returns. There is like a thousand grammar-ish things past the basics that you need to know in order to comprehend the language: it is pointless to attempt learning them all preemptively because you simply won’t be able to hold it all in you head unless you practice encountering them. And learning just a few dozen of those won’t make any difference (ocean, drops, that sort of problem). You will have to look advanced grammar up as you encounter it (or re-figure it out on your own) even if you “pre-learn” it, probably time and time again, until you finally absorb it for good. Might as well not waste time learning things that you probably forget before the “real-world” encounter with them.