Hiragana & Katakana
Spend 1 weekend (2 if you can’t), make flashcards, and learn all of the Hiragana and Katakana. If you can’t initially memorize them in a single weekend, it is best to stop now – those ~50 characters will look like nothing compared to the 2000+ Kanji you have left to learn
*Goal: Learn the whole Japanese alphabet (46 characters) in 1 weekend