You may have a hard time just for being a teenager away from home, going through culture shock, that sort of thing. Just remember that Japan is 98-99% Japanese. That means that they may know black skin and hair and celebrities from pop culture, but they may have never seen black people in person, up close. This could elicit a variety of responses from people. Most likely you will be stared at. Some will be too shy to speak to you. Some will want to practice their English on you as much as you tell them you want to practice Japanese with them. Some might even want to touch your skin and hair. (Even my Asian American friends in high school would stare at my arm hair because of being mixed I had tones they did not have.) You will be different so people will be curious. If you've never been to somewhere where you were the only person who looked like you, it can be quite a shock. I've had an old woman in Tokyo stare at me really hard until finally she managed 2 words in English. That was her thinking face. I didn't realize. I was so shocked I didn't even answer, even though I speak Japanese. My trips back as an adult have been so much better than my childhood rebel days.
I'm half-Japanese, female, used to live there. I moved there and left when I was younger than you. I'm not half-black but one of my classmates and neighbors was. We never spoke, strangely. But that's how kids are. He was a loner. It was an American Christian school full of military children and half-Japanese of all sorts. I imagine he was probably bullied at public Japanese school (I was too) and ended up having to go to the American school. We lived in one of the best places to be foreign because it was Okinawa, an island with a heavy American military presence. There was American tv, radio, and people all the time. Yet, people stared at me, threw rocks at me, called me names, picked fights. Children can be cruel. Children can also be wonderful. Some were very happy to talk to me, just in awe to hear me speak English, would take me to their English tutoring sessions, etc. Your experience may not be as bad as I had it at times and I do not want to discourage you. I think it will be a wonderful experience. Just realize that Japan is sheltered and act like an ambassador.
I have never been to Fukuoka and I don't know where in Fukuoka you will be but one of my good friends from Fukuoka went to a private school that did exchanges with America so I would like to think there are pockets of people who have more international experience, interest in English and Americans, and those people will be good ambassadors for Japan as well for your experience.