(how to live in Japan)(略)
First, polish your Japanese to N4-N3 level, or at least to where you can hold a basic conversation. As a language student, you'll have fewer options for supporting yourself, if you didn't speak fluent Japanese. If you're born as a citizen of an English-speaking country and you look white enough (yes, Japan is still kinda prejudiced like that), then English-teaching jobs would traditionally be your easiest way in. Otherwise, you'll be asked to prove your English fluency with formal credentials (TOEFL or IELTS for example).
But even that is not looking too good right now. Especially since Japan is currently plan to show themselves that they're "tough on immigration", because of their newest PM. The Japanese themselves (outside of Tokyo, tourist areas, or US' Okinawan base) didn't experience much trouble with foreigners, but some bad actors online had roused the perception that Japan is overridden with unruly immigrants. I rare cases, unruly animals like Ramsey Khalid Ismael (Johny Somali) had exacerbated that perception even more. Japanese youths are not racist, but the elderly oldbags (60 yo above) in charge of their society, are indeed full of racist nationalists. Particularly the enemies of humanity called
Nippon Kaigi. Therefore, if you currently didn't speak a lick of Japanese, I'd suggest you to polish up your Japanese for a few years FIRST, before even attempting on securing a student visa.
Your best bet is to have a copy of the bank account of someone who's willing to be your financial guarantor, just to receive the visa to get there. After you arrived there, you'll most likely will need another guarantor (this time, an in-country guarantor). When living in Japan, you'll need a guarantor for nearly everything you do. Creating 印鑑(いんかん)which is their official method of legal signature, opening a bank account, setting up your phone and internet service, renting a room, getting a part-time job, etc. Everything requires a guarantor, especially for renting a room.
This is because they really wanna know who's gonna be responsible, should you default on paying your bills. In Japan, homeless people are viewed as lazy dregs of society that's even lower than an animal. Traditionally for a Japanese native, their guarantor would be their own family members. If you don't have one, then you'll need to hire a "guarantor company" on top of all the bills). It's predatory if I do say so myself, but you can raise those complaints towards their hyper risk-averse societal customs (which was caused by the infamous real-estate bubble).
Paranoid and outdated mentality is why people said that doing business with the Japanese is hard and cumbersome, which directly contributes to their lack of economical growth. "If you actually have a financial guarantor, paying all these extra expenses would be easy, right?" is their mentality. I'd say BS to that, especially to those bastards from NHK fee collectors, that'll come to collect money from you (even if you doesn't own a single TV). Unless you're a student, you can't exactly refuse these extra fees (extortion) from those stupid NHK people (unless you wanna risk your visa), and they know it. In japan, immigrants are there to be financially exploited.
Living costs in Japan (especially in Tokyo) is VERY high, and is steadily rising. Because of it, even homelessness affects native Japanese themselves (and their aging population). It'd best if you live in the outskirts of a big city. For Tokyo's peripheral area, that'd be the SIC prefectures (Saitama, Ibaraki, Chiba) where the prices are more reasonable. You can just take a train to Tokyo if you want to, their train network and punctuality is first class.
For the duration of stay, they'd only allow up to 2 years AT MOST, before you have to renew the visa at their immigration offices. Failure to do so, would make you an illegal immigrant. If possible, you'd want to renew said visa at an office that's relatively inconspicuous, during chill hours (so the officers would be more lenient towards you).
If you're gonna live there as a foreign student without any significant financial support from anybody, you'll live to work and study. There'll be no leeway to play around whatsoever. If by some miracle, a Japanese company would hire you (as an English-teaching school, for example), you'll live to work. Lest you'll risk your visa not getting renewed AND lose the staff lodging they provide for you. There's a reason why in Japan、過労死(かろうし)"death from overwork" is a thing.
If you're very diligent with your studies (which is kinda hard if you're also supporting yourself), you might reach level N2 from zero, within 2 years. But I'd say that this is extremely farfetched, because those who managed to do it, are quick-learners who receives significant financial support from relatives whom also lives there (so they can focus on their studies). I'd personally say that
around 4 years is the more realistic estimate to reach conversational-level proficiency in Japanese.
Make that 6 years, if you've never been exposed to anything remotely Japanese, or your native language is English. Japanese is one of the hardest language you can learn, if you're starting from English.
If you want to learn Japanese, then start NOW. Immediately, little by little. You'll be investing the next 3-4 years of your life, in order to learn conversational Japanese. Add another 1-2 years on top of that, to be able hold a sustained conversation. This is just the language alone. You'll have to immerse yourself into the culture too, if you want to have something to talk about with the people around you. Japan is still an insular country where you'll have to learn to adapt to them.
It's not easy, but it's worth it. You can try to practice your proficiency in this Japanese Chat section.