>>46514554Mastery of kana first is absolutely critical, after that you can decide if you want to just do things like watch JP clips and read JP hololive tweets and posts on futaba's hololive board or something ( may as well learn while using content similar to what you want to watch) or if you want to start SRS vocab/kanji training like with Anki / Duolingo(lol) / wanikani etc.
Reading Holo-related stuff will result in gaining relevant vocab for Holo streams faster but probably isn't the most efficient.
If you're really into it the active learning side of it and don't want to be passive, you can be looking up words you know they're probably saying by items you're seeing on screen in a stream (i.e. a variety of common words in a minecraft stream like hashigo, ashiba, tetsu, sekitan, etc).
Doing some basic grammar can be pretty critical too, since you may have seen all the wonderful times when you hit an Auto-translate on a tweet and it spits out the literal opposite of what the tweet actually says.
If you love manga though, then manga with furigana is great.
It's going to be a massive time investment no matter what learning approach is used, unless you already know Chinese or something then its apparently a fair bit easier.