The world of Onyx was normal, with its sky cars and regular air travel. The three moons revolved around the sun, until one night. That was the night the moons never appeared, the sun still high in the sky and by the the next morning, everything would change forever. Hyeongjun had heard that things would change, and now things were, right after a strange man had shown up, speaking of a planet called Earth, a place he would take them all to. 

X1 consists of 5 members from the 20th century and 6 from the 21st. Those 6 are bound to get in trouble from time to time. Their hyungs are used to it by now.