Reddit reviews Japanese Tutor: Grammar and Vocabulary Workbook (Learn Japanese with Teach Yourself): Advanced beginner to upper intermediate course

More than likely the light novels (7 and 8) will be officially translated by the time you're able to read the untranslated version.

If you still want to learn Japanese though, my best advice is to search around on your own and see what works for you. What I've found works for me has been:

Free Stuff:

First memorize Hirigana and Katakana (Japanese has three alphabets - Hirigana, Katakana (for loan words), and Kanji. Hirigana and Katakana are close to the English alphabet while Kanji is more like pictograms (for example, eye <3 u)). Write them in the margins of notes your taking, buy a set of post-it notes and write down the hirigana and katakana tables every hour or so, and you'll learn it in a few days Certainly less than a week.

For kanji, wanikani (https://www.wanikani.com/dashboard) is a good idea to get started on early (it's slow going at least at first, but a nice review tool - learn the kanji and example phrases on your own if it's too slow). (edit: Actually $10 per month after the first three levels (~1 month to complete first three levels). edit 2: There's a coupon for 50% off forever floating around though.)

Other than that, there are pdfs of the textbook Genki I (link to amazon) floating around (or you could pay $80ish for the textbook and workbook). This is the textbook the majority of people use, and it's basically your standard textbook. The stories of Mary and Takashi are awesome though and pretty fun to follow.

Learning a language requires you to learn a whole host of new grammar rules (Japanese has a good chunk with no equivalent in English) and thousands upon thousands of vocabulary. Tae Kim's Grammar Guide is typically pointed to for those who want to learn the grammar quickly, or have a resource to look at as you encounter new grammar.

Youtube videos. Puni-Puni, and others are quick to watch and really good review.

Watch anime, read manga! It's either very low-cost, or free, and exposes you to the language. You can hear or read the grammar structures your learning about, or see kanji in action. Likely since most are geared towards japanese middle-school-age to high-school-age students you won't be able to understand the vast majority of what you read or hear (without subtitles or translations), but you'll be able to get the gist of it. Here's a youtube channel that takes a sentence or two from currently-airing or recent anime and breaks it down. Also, here's a newer subreddit doing somewhat the same thing.

Lower cost stuff:

I used the workbook "Japanese Tutor" to get from the beginner to intermediate stage. It's $20 but was a very nice way to work my way through the beginner stage to intermediate.

Japanese Graded Readers is a great way to practice reading. They're kind of like scholastic books you would find at book fairs in elementary school. They don't use complex sentence structure or complex words (or complex kanji in japanese's case), and are designed for foreign language learners (so the topics are more adult, less "The dog ran. The cat ate. The bug couldn't swim."). I recommend you start at Level 1 since Level 0 is more about learning odd vocab. You can understand Level 1 books in about 2-3 weeks if you spend around 2 hours each day studying. You get 5 books (15-25 pages each - which is just enough so you don't get tired ever so slowly reading them) for $30.

High cost stuff:

Rosetta Stone is a nice way to learn vocabulary and practice hearing the language, but it's costly at $170-$200 (for all 3 levels - 150 hours). If you have a friend who can loan it to you to try out (or split the cost with) it's a really nice tool since it teaches vocabulary of objects you see in daily life, and you'll be able to look around your house or city and have a word for a good chunk of things.

It isn't online (maybe there's a version out there floating around, can't say I've looked), but I bought this book a while ago to use for some drills outside of the textbook. It contains all the answers so you don't need an extra key, and like Genki it stops using romaji early on. It's pretty solid if you want some extra practice using another book for variety. The only downside is that there aren't any listening comprehension exercises, unfortunately.