Quoted By:
I focused on learning to read, understanding by listening kind of came naturally with it. I don't know how you'd do it the other way around. Also I didn't learn for vtubers, I learned for manga and games years ago, plus I was just bumbling around on my own and not following any established method or sequence.
I memorized katakana and hiragana (pretty much already knew it from years of being a weeb) then learned grammar from Tae Kim's Guide to Japanese (it's a website, google it). For kanji I used James Heisig's Remembering the Kanji, literally just found a pdf of the first volume online, never bothered with further volumes. Then I just dove into some text heavy games that I wanted to read through, painstakingly translating them for myself. Whenever I ran into a kanji I didn't know I'd look it up through a method like SKIP code or just stroke count and add it to my notes with Heisig-style reminders so I could reference it next time I ran into it.
I found it most useful to have both text and audio for practice, so games that are fully voiced or anime with Japanese captions were great.
