Reddit reviews Remembering the Hiragana: A Complete Course on How to Teach Yourself the Japanese Syllabary in 3 Hours

Do not pass go, do not collect 20,000 Yen, but get this book, and when you master that, get the Katakana book and the first two Kanji ones. When I was first stationed in Japan in '91, I bought that in the American bookstore on base and read through it. Twelve years later, when I came back, I still knew most of my kana, and when I relearned one I'd forgotten, the mnemonic came back as well. I'd recommend having a little of the language first before doing the Kanji book, but all four are irreplaceable tools for that language.