There isn't anything special - I have not used the public showers you mention as I tootle straight off to the hotel, but if they are still there, that would be your only option I think.

There are a few threads on the lounge facilities at NRT - to recap (because I haven't worked out how to paste a link to the other threads ) its shared with Northwest and all the other Skyteam airlines. Personally I don't care for it - bit of a barn and food and drink not great (though others have disagreed with me on this), but it is comfortable enough, relatively peaceful and well equiped with PCs etc.