If you have a bachelor's, teaching English. If you have a masters or sometimes just a bachelor's plus celta or equivalent (aka not just any tefl) and teaching experience (usually post-secondary required), you can teach university level in your educational field. Without education, modeling is sometimes an option. But that only usually works if you can get picked up by an agency in your home country and they sponsor you to go their (aka, you need to already be a model in your home country with an agency who can get you into Japan). After that, unless you are from a nearby southeast Asian country and can get in through technical schools labor work type visa (WHICH I HIGHLY DO NOT RECOMMEND due to the fact of how the workers are often prevented from leaving and forced to work unskilled labor without learning what they came for), but other than that, there are not many options. If your Japanese level is N1 (maybe n2, but not as much) or above, you can do translation, but that can also be done remote. Getting into a Japanese company requires native-level or at least n1+ (n2 in some cases) level proficiency. AKA you will need to be able to do business and speak formally without needing assistance.
The main reason why living long-term in Japan is difficult, is that you will need a work visa, and for that, you will need to be sponsored by a company. Part-time jobs don't sponsor people (cost etc) as far as I know, so the only option is a full-time real position, and you will need to speak Japanese for that.
I also highly suggest visiting Japan on a tourist visa first (90 days, if your country has democratic relations with Japan). The actual place is not at all like dramas or manga. Not saying you believe that, but just from my personal experience, it is much different than the perception it gives off online. When I was there, many of the foreigners I knew were quite disillusioned by it and had inaccurate expectations for what Japan was actually like.
Hth. If you really want to go, I suggest getting a bachelor's degree and using that time also to study the language thoroughly. With enough dedication, 4 years can get you to N2 level, and even N1 for some. Going to Japan to live, is a business decision, not simply a personal one. Japan doesn't just accept people in, because you have to bring something useful to them. Without any credentials or practical/work skills, it will be very difficult to obtain the necessary visa for long-time stay.