Time needed in Narita for plane change

We will be traveling from Hiroshima back to the United States with a stop and plane change in the Narita airport. The flight from Hiroshima to Narita is on IBEX airlines and the flight from Narita to the U.S. can either be on Al Nippon or United Airlines. The layover time is 1 hour and 20 minutes. I do not know if we will have to recheck our luggage at Narita and am worried about the amount of time between flights. I would greatly appreciate any advice on this.

Advice: don't worry.

Did you book two separate tickets?

1 hour and 20 minutes sounds very "tight".
Upon arrival you need to collect your luggage from domestic terminal; move quickly to international terminal for check-in; pass the immigration, expect a long queue due to rise in overseas tourist numbers; boarding call would normally start 30 mins before the departure time. If you manage to pass the immigration in time, you would be still doing "amazing race" to get to your gate which could be a few hundred meters away.
If I were you, I would try to get an earlier flight from Hiroshima, extra hour would make a big difference.

There is no "domestic terminal" or "international terminal" at Narita.

Upon arrival you need to collect your luggage from domestic terminal; move quickly to international

Possibility of arriving at terminal 1, and departing from terminal 2 ?

Can the wait time at immigration really get that bad? I always fly into Haneda for the sake of convenience which obviously has less domestic traffic than Narita, but still I've never really had more than a few people standing in line in front of me. From leaving the plane to standing on the monorail platform is usually 10-20 minutes. Is it really that much worse at Narita?

Here both flights will use Terminal 1 since the international flight will be on ANA or United (both in StarAlliance) and the domestic one will be on IBEX, which is a close partner of ANA as well.

In general all partner airlines are in the same terminal, so a terminal change is only needed if you have a weird itinerary (especially if you book both flights separately).

I always fly into Haneda for the sake of convenience which obviously has less domestic traffic than Narita.

Haneda is Tokyo's domestic airport and the ratio of domestic to international at Haneda is probably ten times that of Narita.