If you purchased the ticket on ANA website at same time then most likely it is under one ticket, even though you used multiple destinations function. Any case you are transferring from NH (ANA) to NH (ANA) so should really not make any difference at all if tickets are under one or two as far as you are concerned.

Minimum connection time at NRT for NH (ANA) domestic to NH international is 45 minutes. Both NH domestic and NH international use Terminal 1 South at NRT. Upon arrival at NRT from domestic flight, there is a passport control dedicated to passengers transferring from domestic to international. This passport control is separate from main passport control where NRT departing passengers use. However, most likely big portion of passengers on ITM-NRT flight are transiting to international flight at NRT, so can be little bit of line forming at a passport control since good number of people on your flight will be transiting to international flights also. Your transit at NRT of 2 hrs. 25 min. should be more than fine.

At ITM there is a check-in area specific for passengers transiting to international flights at other airports such as HND and NRT. Check-in counter no. 11 of NH check-in at ITM is specifically for such passengers and that is where you will check-in at ITM.