It's good that you spend part of your essay talking about how you yourself came from a diverse background but there's a few problems.
You spend all of this doing that and honestly, most of it is just you repeating yourself. You describe this background well but what did you learn from it? Give me some specifics on how it made you stronger.
My experience at an international school can contribute to USD community. Being an international student might be difficult but I want to show other students new perspectives and cultures that they never knew before. I want people to understand more about Japan. There are countless things that we all do not know yet and I want to accomplish and provide those knowledge at USD. I will bring diversity to USD community.
This part is what you can contribute but I'm afraid that it's way too small at moment and plus, I don't see much of what you can contribute. I understand that you are from Japan and can bring your customs but again, SPECIFICS! Want kind of traditions and knowledge have you attained from your Japanese culture that you can bring to USD?