Can I marry a foreigner who enters the U.S. with only a passport?

I want to marry my boyfriend who lives in Japan. He does not have any sort of visa, only a passport. I live in Nevada. Is it possible for him to come to the U.S. with only his passport and marry me? Or if you can offer an easier alternative to make the process less complicated so he can permanently stay here. That would be great! Personal experience would REALLY be helpful and encouraging! Thank you! ○(^____^)○ (we have been together for 2 years now. AND we have documents, emails, letters, gifts, flight itineraries, receipts, etc. to submit to USCIS just in case.)