Everlaster tells the story of a boy named Mason, who, while playing in his backyard late one night, encounters a man named A.B. Laster — standing on the edge of a large, old-fashioned train that’s levitating in midair.

But this Flying Train isn’t just a train — it’s a massive, hotel-like building inside with a grand hall and many rooms, which is home to six residents who have nowhere else to go below.

However, this train has it's own story. The Flying Train is possessed by a shadow demon named Nox, who made a deal with A.B. to give his family a home in exchange for his freedom.

A.B. is bound to the train forever, and he is incapable of leaving.