But before you jump on a train, think
twice. In Japan NOBODY speaks or understands English. So, it might be
better to stay away, when you travel alone and also don't spreak or
understand the local language.
At night it seems the Tokyo Narita airports closes. And they even shut
down the lights. If you try sleeping overnight at the airport, you will
probably end up in a dedicated area by local police, where they might
ask you for your passport once every hour all night long (and wake you
every time over and over again). The good news: there seem to be several hotels
near the Tokyo Narita airport terminals.