Nether Express is an Evil Symbol from Disgaea 4: A Promise Unforgotten. You can unlock the bill by making a unit walk at least 10 spaces in a single turn. This can be easily achieved by assigning a Thief or Masked Hero into the Nether Shoe Lab and giving them some footwear. The Nether Express allows you to set up a train station, complete with train tracks from your Base Panel, that units are able to move to from the Base Panel without using up their Move command for that turn. The path to the station must not be blocked by enemies. The unit assigned to the Nether Express Evil Symbol gains a spell called "Station Creation", and higher levels of it allow you to place the train station base panel closer to enemies. This can be useful when grinding to put units with low movement or short attack range within striking distance of enemy units.
Allies that wish to use the Nether Express have to be selected on the Base Panel and are given an additional choice to "Board", which takes them to the train station without using up their Move command for that turn. You cannot immediately cancel a movement to the train station until after the character moves off of it. The train station panel must also be clear before a second character is able to use Board to go there. Enemies do not appear to pay any attention to the train station and can even inadvertantly stand on it.