On one side, it's called a mirror.

On the other side, it's called a window.

We've always been able to pass through,

but we've never had the will to try hard enough.

On one side, it's expected to follow you.

On the other side, you're expected to follow them.

Exactly.

To the point.

Not one mistake.

D.O. grew up to be a singer. A vocalist. His life was near perfect in his perspective and nothing could get any better. It started when he accidently twitched his hand. It became concrete when he sneezed while doing his job. Now they both are in a lot of trouble.

Kyungsoo grew up to be a mirror. Just like everyone in his messed-up society. When he wasn't stuck following his 'copy' he was being torn up by life. It's not only his job to fake a barrier between the two worlds, it's his job to protect his other self. Protect him from the complete and utter horror of the other world. It started when I, Kyungsoo, twitched my hand. It became concrete when I sneezed while doing my job. Now we both are in a lot of trouble.