The ANA Lounges at NRT not only offer showers but also sleeping areas with reclining chairs ... they open 6:30 AM though untill midnight. I took a four-hour nap there just yesterday during my 12-hour layover ... OT: the one on the second floor below gate 43 is an excellent lounge where they offer everything United's lounge offers plus Suntory Yamakazi 12 year old single malt whisky and 6 diffrent hot noodle dishes.
^^^