Mystery lights in Tokyo sky.

http://www.asiaone.com/asia/mystery-lights-appear-over-tokyo-sparks-fear-and-confusion-among-netizens

My best guess for this is either a lightning ball or earthquake light.

A lightning ball moves in a slow and abnormal way.  Please look at the lightning ball picture below.

Earthquake lights can look similar to lightning ball too.  Please see the picture below.

If the strange light is related to an earthquake, then Japan is in trouble because there'll be an impending earthquake soon.