getting J-citizenship after age 22

I am half Japanese half American, raised in Japan but born in USA. Unfortunately and unlike most other half J's, I never held dual citizenship - only US citizenship. I am now over 22, but wanted to get a Japanese citizenship for many reasons. Does anyone know what the process is for obtaining J-citizenship in my case? Am I considered a foreigner and have to follow the naturalization process, or will it be a different form of claiming citizenship? Will I be forced to renounce US citizenship at the time of this application as well? I've never met anyone in the same situation as me, every other half J's I've met have had dual nationality since they were young. Any help would be appreciated!

Am I considered a foreigner and have to follow the naturalization process, or will it be a different form of claiming citizenship?

Yes, you're considered a foreigner and you have to go through the naturalization process. However, because your dad/mom is Japanese your PR/naturalization process will be expedited.

1.) Get a Child of a Japanese visa.
2.) A year later you can apply for Permanent Residency.
3.) Two years after that you can apply for citizenship.

Will I be forced to renounce US citizenship at the time of this application as well?

You won't be forced to renounce your US citizenship but you have to swear to renounce it within 2 years after naturalization.

As many people will tell you, there aren't very many benefits of having Japanese citizenship over PR. You'll be able to vote and won't have to get re-entry permits but that's about it. If you were from a developing country you would have an easier time traveling with a J-passport but you're from the US.