Between looking through this and your other thread, uJapanese language school requires diploma?v, I think you might be somewhat confused as to how the work visa system works.
It sounds like your plan is:
1. Enroll in a Japanese language school that will give you a student visa and come to Japan.
2. When the student visa expires, get hired by your tattoo mentor's family for some kind of non-tattoo artist work, then get a work visa and work as a tattoo artist.
But work visas don't work like that. It's not just a matter of saying to the Japanese immigration bureau "I have a job in Japan" and then they say "OK! Here's your work visa!" The work visa is something you have to apply for, with the person/organization you'll be working for acting as your sponsor. In addition to paperwork that the sponsor has to file, they have to meet certain responsibilities (primarily showing that you, specifically, are a necessary employee and that you'll be earning enough to support yourself).
Again, it's an application process, not a rubber stamp one. It's not as simple as the company saying "We want to hire this person" and a visa automatically being issued. Generally, the immigration bureau needs to be convinced that the job makes a positive contribution to Japan's economic or cultural environment, and that the benefit is enhanced by having a foreigner do it. But if you have a less-than-high-school-level education (as mentioned in your other thread) and only one year of Japanese classroom instruction, it's unlikely that you'll be able to perform a job that meets those requirements.
In addition, work visas are usually tied to a designated field or industry. Not working in the field your visa is for, and/or working in a field outside of it, could be seen as visa fraud, depending on the circumstances.
You've also mentioned that you're a licensed tattoo artist, but your license in the U.S. isn't going to qualify you for that sort of work in Japan. Especially since tattooing is a quasi-medical procedure, you're going to need to get certified in Japan, and I'm guessing taking the test in English isn't an option, so you're going to need to get your Japanese skills, in a specialized vocabulary field, up to a pretty high level.
Sorry if this sounds overly negative, but you've got some serious roadblocks in your desired path, and you might need to adjust your course a little. Also, while I don't mean to be overly suspicious, it seems like you've got a lot of your plan riding on getting a lot of support from your mentor (a place to live, a job that gives you enough money to support yourself, a work visa), but you still have a lot of questions for us Internet strangers about the specifics of finding a job and getting a visa. Those are things you might want to discuss with your mentor, and if he can't give you concrete answers, you might want to look into some sort of backup plans/safety nets in case he doesn't end up being able to provide the support you're relying on.