Mixed Nationalities Couple in Customs

Hello, all. I’m an American and my boyfriend is Italian (EU citizen). We’ve planned a trip to Japan this summer and I want to make sure we have everything we need to go through customs, including necessary paperwork and hard copies of things immigration agents might ask for. As a result, I would like us to go through the immigration process together. Are we able to go through the same customs line once we land in Narita? Often Americans and Europeans are forced to separate, but I would think that doesn’t necessarily have to be the case at Narita. I tried researching via google searches and the airport’s website and couldn‘t find anything. I would appreciate any help, thank you!