Hi
I have found the following:
http://www.jal.co.jp/en/inter/lounge/topics/2003_06/
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Lounge service for passengers connecting between international flights and domestic Japan flights is provided
1. When making a same day connection from a JAL group domestic Japan flight to a JAL group international First/Business Class flight.
2. When making a same day connection from a JAL group international First /Business Class flight to a JAL group domestic Japan flight.
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Your conncetion is case 2, so I guess you probably need to show them your ORD-NRT business class boarding pass
Narita domestic lounge has shower facilities and a business corner, and it gives you free internet access (inquire at the entrance), according to JL's Japanese site.
kojiro