"Get a MEXT scholarship so you won't have to worry about anything else" is a pretty low-percentage shot at studying in Japan. Yeah, it's definitely a nice thing if you can do it, but it's far from the only way to study in Japan.
So getting to Rakib's questions:
●「I was wondering in which way i could possibly attend Highschool from the 1st year in Japan when i am 16 years old with no relatives living there, and in what ways could i find a guardian or of the sort to vouch for me living and studying there? I could guess the expenses and save up (which i can). But What are the LEGAL Requirements that are needed and can it possibly be done?」
As a 16-year-old, you'd be a minor, and so the legal requirements you'd need to meet are a visa and a legal guardian in Japan. Let's start with the visa.
Basically, if you're not a Japanese citizen, you'll need a visa to live in Japan. In broad terms, there are three types:
a. Dependent visa - i.e. you're the child of someone who has a visa to live in Japan. Since your parents don't have Japanese visas, this won't be applicable to you.
b. Work visa - This also won't be applicable to you. As a minor, you won't be able to do the sort of full-time work that's applicable for a work visa.
c. Student visa - This is the one you could possibly obtain.
So the question becomes how to get a student visa. Student visas are dependent on acceptance to a school/study program in Japan. In other words, you have to find a school/program, apply, and get accepted before you can apply for the student visa. You can't just apply for the visa first, then figure out what school/program you're going to attend afterwards.
This is why you'll hear people say there is no "I just want to study in Japan" visa. Even if you were to somehow find a Japanese family willing to vouch for you and provide you with a place to live, that isn't enough to get you a student visa if you haven't also been accepted by a school.
So now the question becomes how to get accepted by a school. For this, there are a few major paths:
a. Apply at a school that has no study abroad/exchange programs: This is going to be the most difficult path, and likely impossible. You'd be asking a school to sponsor a student visa for you despite not having any experience in the process or support staff for it. It's far beyond what a school could reasonably be expected to do.
b. Apply at a school that does have a study abroad/exchange program: This is the path that's going to give you the best chance of success. Schools that have such programs are versed in the process of applying for/sponsoring student visas, and also support staff to help with the transition to life in Japan and any problems that might arise.
You mention you have talked to your home country school's counselor and the Japanese embassy and they haven't been able to help you. If that's the case, you should next try contacting applicable schools in Japan.
●「In what ways could i find a guardian or of the sort to vouch for me living and studying there? 」
This generally isn't something that you would do yourself. Instead, schools that sponsor student visas are often the ones that do this, once the student has been accepted and committed to coming to Japan. There are non-school affiliated homestay organizations, but these are generally for shorter stays by travelers, not people living in Japan and going to school there full-time.
●「My family is not rich but i think we can afford to have me sent there and attend high school and i was thinking if i could legally get a small part-time job to support paying for the homestay at least.」
You mention getting a part-time job to try to finance your living expenses, but be aware that in Japan high school is not part of legal compulsory education, and even public high schools require tuition.
● While there are exchange programs for high school students to Japan, you might be better served by waiting until college to come. Forgive me if this sounds presumptuous or rude, but the fact that you're asking these questions on an English Internet forum instead of utilizing Japanese-language sources makes me think that your Japanese-language skills aren't at a particularly high level yet. If so, regular classes at a Japanese high school really aren't the place to hone them.
As a largely homogenous country, the vast majority of the high school-age student body in Japan speaks Japanese at a native level. It's one thing if a non-Japanese-native student has some pressing reason to be attending high school in Japan (such as having to live in Japan because of their parents' jobs, being a refugee, etc.), but it's another for someone to attend a Japanese high school and slow down the speed of instruction just because they're interested in Japan and want to live there.
This is another reason why you should be looking for schools that offer study abroad/exchange programs. Those schools are set up to provide support to the student, and also to teachers in structuring lessons that allow the Japanese students to get the education they need without leaving the foreign student confused and frustrated.
As an example, imagine if a Japanese student, who speaks Japanese but very little of any other language, suddenly wanted to start attending high school in Bangladesh. If there was some reason he had to, or if it was going to be a short-term program, then sure, people in the school (teachers, administrators, other students) would probably be willing to help out however they can. But if he said "Hey, I don't speak the language, and I could have just as easily gone to school in Japan, but I think Bangladesh is cool, so I'm gonna go to school here and you need to help me," it's a different situation.
Also bear in mind that even if you like Japan so much that you're willing to get below-average grades while struggling with the language, the teacher will still have the pressure/negative performance reviews from having an underachieving student.
Because of that, unless your Japanese is at a level where you feel you could jump right into reading textbooks, writing reports, and having classroom discussions all in Japanese (and that goes for humanities subjects like Japanese literature and history too, not just math and science), you're really better off looking for a short-term study abroad program instead of trying to enter a Japanese high school as a regular, full-time student, and perhaps looking for a more intense study-in-Japan experience as a college student.