Dual citizenship for US and Japan

I am a Japanese american (age 20) and I want to live in Japan for maybe... about a year. I currently have a dual citizenship of Japan and US. I was wondering, in order to stay in Japan longer than 90 days, do I have to make a Japanese passport to prove that I have a Japanese citizenship? but how do I make a japanese passport if I dont live in japan? I dont think I have to get a Visa or anything like that because I have the citizenship. I know Japan doesnt allow dual citizenship, and you have to choose by the age of 22. If I just stay right before I turn 22, I wont to lose my dual citizenship right? I just want to have the experience of living in japan, but i dont know how to do that without losing my US citizenship. so many questions, sorry! and thank you :)

If you are a Japanese citizen, you must enter Japan with a Japanese passport. If you don't have one, contact your local Japanese consulate.

But can i even get one if i have dual citizenship?

yes

You wont "lose" your US citizenship regardless; you have to actually renounce it and fill out paperwork to give it up. The issue is the Japanese citizenship; as Japan technically doesn't allow dual citizenship, if you don't "choose" Japanese citizenship by age 22, the Japanese government assumes that you don't want the citizenship, and you do lose it.

But I say "technically" because you can "choose" your Japanese citizenship and just keep your US as well, and as long as you don't have any tax issues or commit crimes that would bring your dual citizenship status to the attention of the Japanese government, it's pretty much a "don't ask, don't tell" situation. I know a number of dual citizens who have no problem using both.

Definitely get your passport. You can do so quite easily, as Firas said, by contacting your closest Japanese consulate and getting the necessary documents and procedure from them.