You can fly cheaper than train, if price is important. From ITM to NRT you can get a discount flight for tourists only on JAL or ANA.
https://www.jnto.go.jp/eng/transport...r-service.html

For a much greater discount, you can fly from KIX to NRT on an LCC. For example:
Home | Peach Aviation

Check-in for domestic flights in Japan can be done up to 30 minutes before departure.

I live in an area between Osaka and Kobe, and always fly from Osaka to Narita if catching an international flight out of NRT. For me it's just easier than catching and transferring trains, and walking through stations with luggage. On the other hand, from Kyoto it takes longer to get to either ITM or KIX. Also, I need to catch a local train and transfer at Shin-Osaka if going by shinkansen, while shinkansen stops at Kyoto station, which might be easier for OP to get to. The train isn't a bad option and maybe the best, but wanted to highlight some other choices.