Woohyun had lived with a strange ability. 

He could see an invisible tattoo that was much like a barcode with some numbers on it. He didn't understand at first, he was only 10 when the sudden sight came. Woohyun was in his neighborhood's playground and Jonghyun was bullying him, kicking him on the stomach because he lost something that was Jonghyun's - and it was only a small, cheap ball. Even so, Woohyun knew that boy had never liked him and he would be furious when he found out, so Woohyun had pretty much prepared for the outcome. It was more than he expected though, because Jonghyun beated him up with his so-called friends who didn't like Woohyun very much, either. The barcode was there on Jonghyun's neck. Woohyun caught the numbers and it was written 21072002. Being the dumb kid he was, he didn't really care and only asked himself why did jonghyun get a strange tattoo? 

A week after the incident, Jonghyun died in a car crash. And it was July 21st, 2002.

Then, he met Kim Sunggyu; an adorable guy who was two years older than him.