What flights are you on (into NRT and connecting to)?

There are 2 terminals at NRT which are security controlled (ie cant freely switch between them back and forth). Depending on the carrier of your flights you may not have access to RCC or SilverKris lounges. Also the lounges operate different opening hours related to their flight times.

UA and SQ operate from one terminal, NH TG and OZ operate out of the other.

For example if you are arriving on UA and connecting to NH then as transit pax you wont have access to terminal with RCC (other than the passage to the airside bus to change terminal).