Flash back 5years ago

When Seohyun still a freshmen in high school, she was still that beautiful but she wa a so-called nerd too. She got bullied by their kingkas and queenka almost everyday.

And Jin was her senior, he was still the same as now, cool image also a lot of fangirl. They don't know each other until one day, Jin's ex tried to hurt Jin because he broke up with her.

School end time, all the student storm out the school. Seohyun, she need to walk to yard near his school to hide her real status as a rich girl from the others. Then she saw a boy about 10meters away from her walking with a girl follow behind him, first she thought it's nothing, suddenly the girl take out a small knife from her pocket and run toward the boy.

"Omo! Watch out!!" Seohyun shouted and quickly run to that boy, he tried to found where the voice came from. He turned away and saw a girl was covered him with her own little body.

Hyuna shocked and pulled back, so the knife didn't stabbed deep on Seohyun. 

"Yah! What are you doing? Are you crazy?!!" Jin shouted at Hyuna, she then run away panickly.

Seohyun fell sit on the ground, Jin squad down and ask her condition. Seeing a wound at her back, the blood came out.

"Are you okay? Who are you? Why you help me with your own life?" Jin ask her.

"I.. don't know you, but... I.. saw.. someone tried to hurt people.. so I.. helped..." then she fainted. Jin quickly take her to the nearer hospital.

"How's her condition?" Jin ask when saw the doctor came out.

"She is okay now, fortunately the wound didn't deeped. And she fainted because of another factor we still need to check it."

"Can I came in?" Jin ask.

"Of course, she already awake."

"Thank you doctor." He walk in the room, Seohyun was layed on the bed.

"Uhm., hey are you feeling better now?" Jin start the conversation.

"Yes, I'm okay now." She didn't dare to look at him in the eyes.

"What is your name? You're a fresh men? Why I never saw you before?" 

"My name is Seo Joohyun, yes I'm a freshmen. I'm a nerd I didn't standing out much at school that's why you didn't notice me." Seohyun said.

"I'm Kim SeokJin."

"I know you, you're my sunbae in third grade. You also got rank 1 every semester in highschool." 

"That's why you helped me?" He thought she was like another fangirls tried to get his attention.

"Nope, I only know your story but not the real person. I never know how're you look like." 

He felt guilty after heard that, she wasn't like a fangirls. "Sorry, and thank you for helping me." 

"I'm curious who want to kill you? I saw her wear a same uniform might be our school's student too." 

"She is my ex, I broke up with her last night." 

Seohyun only nooded her head, didn't want to ask more.

"Rest well, I'll come again. I'll take care you." Jin said then he leave.

Afrer that day, Jin take a good care to Seohyun. And they increased their relationship, Jin shows his true image. He was a kind boy, but he prefer to be look cool because with that no one dare to harm or bullied him.

Another day at school, Seohyun was at bathroom suddenly two girls came near her.

"What?" Then the two girl dragged her to an empty class. She saw the girl who tried to killed Jin was there.

"Why you take me here?" 

"Shut up!" A girl said.

"So you're the one helped my Jin that day?" Hyuna started walking toward her.

She hold her chin up harshly, "what is your relation?!!" Seohyun struggle while her arm was clinged by the other girls.

"We're sunbae hoobae relation, only that." She said.

"You think I believe?! It must be you! Jin broke up with me." Hyuna then slapped her.

"I don't know him really. If you want to know why he broke up with you. Why don't you ask him?" 

"How dare you talk to me like that? You only a freshmen." Slapped her another cheek.

Seohyun struggle to get off, finally he get off. She quickly run toward the door when she tried to open the door. Hyuna come toward her and pulled her hair.

"Ah!!" 

"What are you doing!" Pinned her to the door, she kick her stomach made her fall down to the ground. That time Jin was walking alone and pass the empty room, he heard a girl shouted voice.

"Some nerd was getting hurt again" he thought, he didn't care it all then he heard the voice again, and seems familiar. He take a look from the windows and saw 3 girl were abused a girl

"Seohyun?!" He quickly brag the door.

"Kim hyuna what are you doing!!!" She shocked saw Jin come in.

"I... I.." if you dare to hurt her again, I promise I'll make your life miserable!" He warned her then he carry Seohyun bridal style and left.

Instead took her to infirmary he took her to the hospital, because she was fainted and he afraid might be something happpened to her. Got a lot of attention when the other students saw Jin was carrying Seohyun.

"What is your relation?"  The doctor ask.

"I'm her friend." 

"Can you called her parents?"

"She said her parent was overseas, what happened to her?" He ask worriedly.

"Then I'll tell you, and please inform it to her parent if you can. Come with me." He took him to his room.

"When that time I told you she fainted because of another factor, then we already check the caused. Finally we found it, I want to inform you but you never come again."

"So what is the result?" 

"She expose Leukemia." 

"What is that?" 

"Some type of cancer."

"It will damaged her life?"

"Yes, but not a critical one. If she want to take medicine and check up she will live longer."

"You mean it's uncure?" Doctor nooded, after that Jin went to saw her.

"Seo.." 

"Oppa.."

"I.. have something to tell you." 

"About my condition? I know it well." 

"You really know?"

"I got Leukemia right?" She smiled.

"You already know?" 

"Yes, for a long time ago."

"Your parent know?"

"I never told them, I don't want they worried to me." 

Jin stare at her, he think that she was different from other girls. She need someone to protect her, "from today promise me, if someone tried to harm or bullied you, tell me. I'll protect you."

Since that day, he protect her a lot until he end his high school and enter college. But they still keep in touch, they never told anyone about their relation until now, neither GG nor BTS.

When Seohyun on her last year at high school, her auntie from Australia informed her that her parent was passed away because of an accident. Once again she became upset and her condition became critical. Jin know it and take care of her almost everyday until she back to normal condition.

Since that year, Jin was the one will accompany Seohyun to visit her parent grave. Nobody know Seohyun's condition only Jin and he promise her to keep it as a secret.