We all like to think that we are the sole owners of our lives. However, we don't get to make a single choice according to our own desires. Park Jimin thought his perfect little life was the product of his own passion and work. He was the youngest son of a wealthy family and went to one of Korea's top university. Jimin successfully graduated medical school and became a doctor. On the night of Jimin's 34th birthday, he's hit by a car and goes into a coma. He wakes up to his family singing him happy birthday... celebrating his 18th birthday. 

At one point in our lives, we're consumed by firing passion that seems like it could burn forever. No one, not even ourselves, can stop this fire. Young people are not only beautiful because they're physically attractive but because youth shines so bright that it blinds everyone. Min Yoongi remembers the time when he was boiling with undying embers of firing passion and youth made him invincible. Now he's 34 years-old and bitter with no money or family. There is no more passion, love, and vision left in him. After a drunken night, he wakes up to the voice of his dead mother calling him from the kitchen. His high school uniform hung from the closet... he was 18 years-old once again. 

Loving someone is the easiest and the hardest thing to do. Kim Taehyung used to think love was the simpelst act of mankind. He was filled with love; love for people, nature, family, friends, animals, and even for inanimate objects. There was nothing in this world Taehyung couldn't love. In a way, his circumstance made it easier to love everything becaue the world was naturally kind to a son of wealthy and honorable family. 34 years-old and the CEO of his family company, Kim Taehyung now knows the bitter side of love that he didn't know when he was 18 years-old. One night he gets a call from his secretary and everythings goes blank. Next day he wakes up and the refelction that faces him is of 18 year old Kim Taehyung. 

How can you be honest and loving in a world that abandoned you in the first place? Jeon Jungkook knew his life was doomed since the very first time he realized that his home was made of cardboard box and dirt. There was no place for people like Jungkook so he decided to live his life however the he wanted to. Either way, he was going nowhere in life. Then he meets this annoying rich boy who makes him want to change his fate. Who keeps making him want to be a good guy. Who keeps making him look for the good in bad. For once in his 18 years of life, Jeon Jungkook wanted more than this. Now he's 34 years-old and a judge living comfortably with wealth he never could've imagined when he was 18. He should be happy. He should be proud. But something is missing. On a night before his vacation to France, he finds a letter from 16 years ago and suddenly everything goes dark. He opens his eyes where he finds himself sitting in a nosiy classroom. He was 18 years-old, the darkest and brightest moments of his entire life. 

If life gets hard, just leave everything and run. That was how Jung Hoeseok lived his life. To put it nicely, he prefered peace but if we're being honest he was a coward. He couldn't handle rejection and failure so if it seems to be going wrong, he turned around and ran. Hoeseok was afraid of everything and he didn't have a problem with that because that was just how he lived his life. His family were too busy to care about what he did or didn't do. No one cared about him. Then he became 18 and careless. He didn't care how his life turned out anymore. He didn't care if people didn't like him. He could care less. Now he's 34 years-old and stuck. He's stuck in a job he didn't like, marriage that was clearly failing, and people who meant nothing to him. One night, he's fed up with all this stuckness and packs his bag. Next day he wakes up sitting inside a crowded bus filled with teenagers. Someone next to him taps on his shoulder and he realizes... he is 18 and free. 

Who are we? That's actually not that important but Kim Namjoon wants to know. Not about himself. But about his coworker Kim Seokjin. About his students. About his younger step-brother who he didn't even know existed until few months ago. Namjoon didn't become a teacher because he was driven by passion. He became a teacher because it gave stable salary and was a respectful job. It was right in the middle. He liked normality and wanted nothing but to be ordinary. But things kept happening in his life that forces him to become extraordinary.