Almost a decade years earlier, Krystal had serious pneumonia and had to be hospitalized. Jessica sat next to Krystal's hospital bed in California. Krystal was 10 years old and Jessica was 17.

"Thanks for flying all the way from Korea to see me." Little Krystal's voice was anemic and quiet. She was connected to machines everywhere, needles in her wrist and tubes running down her nose. Her soft hanks of hair flowed under her neck. "I know you're debuting in a few weeks."

"Don't worry about that. I just want to see you get better." Jessica held her hand and rubbed the circle shaped birthmark on her forearm. When Krystal was little, she used to draw on it to make it look like Mike Wazowski from Monsters Inc.

A doctor knocks on the door behind her. He entered and said, "Hi, are you family of Krystal?" Jessica nods. "Can I talk to you for a moment please?" Jessica gets up.

"I'll just be gone for a minute, okay?" She says to Krystal. She nods.

When Sica leaves the room, the doctor shuts the door behind them. "I need to talk to you about Krystal's condition." The doctor says quietly. "We hoped that the antibiotics would work for her pneumonia, but it's just causing more complications." Jessica shuffled uncomfortably.

"Is it viral? Have you tried other treatments?" Jessica asked heatedly.

"We're afraid to use other pharmaceuticals because of the infection in her intestines is getting much worse. She's already dehydrated and we don't want to do anything drastic right now." The doctor's eyes showed pain. "I don't want to alarm you, but if her lungs get worse, we'll have to give her drugs regardless of their consequences. Krystal is a true trooper in spite of all the pain she's experiencing."

He puts a hand on her shoulder and said "She's lucky to have family like you. Sometimes the patient's family can't visit, and when they're able to come later on, it's too late. I wish your sister the best of luck." The doctor walked away.

Too late? The words bounced wildly in Sica's head.

Jessica entered Krystal's room again. "What did the doctor say?" Krystal asked.

"He said that..." Her voice faltered. "He said that you're being very brave and the doctors are doing everything they can to make you better."

"It hurts everytime I breathe." Said Krystal, her eyes fluttering.

Sica started to cry uncontrollably. "Just please.. please get through this. And, and I promise you won't ever get this sick again." Jessica thought about the doctor's words. Sometimes the patient's family can't visit, and when they're able to come later on, it's too late.

She looked at her sister, a fragile, pale girl clinging onto life by a ventilator. As her cheeks glisten in tears, Jessica thinks to herself, 'I'll never do that to you. I'll always be by your side if something happens, Krystal.'

And after one more week, Krystal's condition started improving. Jessica was elated beyond belief and she debuted in Girl's Generation knowing her sister was safe from any harm.

Jessica and Naeun are still sitting on the store bench when Sica tells the news. "Krystal is patient zero."

Naeun's large eyes widen. "Do you mean... she was the first one with the disease?"

"I don't think so." Sica said, sniffling. "Apparently she was bit by another biter. But she was the first one put on hospital record."

"Unnie..." Naeun is dumbstruck. "I'm so sorry."

"Krystal asked me to come with her, to see our uncle in Buyeo." Jessica says, guilt pulsing through her heart. "And I said no."

Her eyes are pained, contrite. "She... she told me she was still afraid to drive on her own because she only got her license a month ago." Sica breathes heavily. "My mom said she died before she reached the hopital." Her last words trail off as she bursts into tears. She arches her head onto Naeun's shoulder. Naeun wraps her arms around her.

"Unnie, nothing was your fault" Naeun says comfortingly. "Krystal was one of my closest friends, I'll miss her so much." Naeun's eyes well with tears too.

As Naeun and Jessica grieve and console each other, they don't hear the rumbling knocking sound emanating from the floor beneath them.

Something from the outside is banging its hands violently on a locked entrance of the store.