[1][2] A manga series was serialized in Dengeki Daioh between January 2000 and May 2003 and was completed by the sixth bound volume.
They exist in train versions, huge ones, with shopping malls and dorms and anything else one would need in an education.
Most students go to standard school trains, to travel around the world for a regular education.
Reiichi, the protagonist, finds himself on the Special Train after literally being handcuffed to Arena, a young female warrior with brutal assassins pursuing her.
The Special Train accepts him and Reiichi finds himself drawn into its adventures, such as having to win two million 'gold' and saving a small mountain town from certain disaster.