Futatabi

Futatabi is an one-shot manga written and illustrated by Kentaro Miura.

Plot
Rick has lived a normal life as a mechanic's apprentice in a world underground. That, however, is about to change as he bumps into a strange intruder who is not quite like anyone Rick has ever seen before. Venus, the intruder, claims to be from another world just like Rick's, though slightly different. With the police after Venus, can they figure out what is going on?