It is a co-ballad song.

The song’s chorus is a wonder of layered vocals and soaring melody. Its dual refrains offer a theatrical sucker-punch, building to a knockout bridge that takes full advantage of the group’s vocal line.

Cosmic Railway it's like a story of two people who haven't really met each other yet but knows that the other would be on the other side of the world.
Like trusting your whole self to that person without any doubt that the two of you are meant to be together.

Color Coded Lyrics by BRelaxion

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