"This is crazy," Hyeon-min said on the way to the hospital. "I have no idea who you actually are."

"Well, you know my dad runs a taekwondo center," Tae-eul pointed out.

"I don't think you needed to tell me that," Hyeon-min muttered, rubbing his shoulder. "The demonstration was enough."

Tae-eul grinned. It was strange being around this alternate version of Shin-jae who had no memory of her; but it was wonderful, too. Hyeon-min was similar in so many ways.

"So what's Luna's last name?" she asked, contemplating the difficulties of impersonating someone based on looks alone. "I'm going to need some basics." She was downing a coffee she'd picked along the way. Sleep was all well and good, but it wouldn't satisfy the caffeine addiction she'd developed in recent months.

"Koo," Hyeon-min replied. She almost spit out her drink.

"Like the Prime Minister?" she choked. Hyeon-min glanced at her, confused.

"Prime Minister Koo," she repeated.

"Never heard of her," he replied. "Luna was adopted. What about you? Are you sure you aren't related?"

Tae-eul didn't know how to answer that. "I wasn't adopted," she said slowly, "But maybe she's a relative I never knew about." Trying to explain the intricacies of inter-dimensional travel at a tense time like this seemed unwise, so she didn't push it further. "No Prime Minister Koo in this world," she mused. "What else has changed?" She didn't know whether the differences were a good sign.

The hospital was busy, but Tae-eul managed to persuade a nurse to give her the details of Luna's last appointment. "I forgot the name of the physician I had it with," she said helplessly. "But I really need the doctor to speak with my boyfriend over there. He's very worried about me." She gestured towards Hyeon-min, who was staring into the distance with such a serious expression it was hard for the nurse to doubt her claim.

They got the name of the doctor Luna had met with and waited outside his office until he had a free slot. "Miss Koo," Dr Ahn greeted her. "I see you've brought someone with you this time."

"Yes, this is my boyfriend Kang Hyeon-min." She tried to ignore Hyeon-min's startled look as she introduced them both. Had he never seen Luna bluff before? "I know this is a strange request, but Hyeon-min doesn't understand why I needed to come here. I was hoping you could tell him the same thing you told me a week ago."

As the doctor began explaining the situation to Hyeon-min, Tae-eul felt her hopes plummet. It was what she had feared. Luna in this timeline was very sick, but it hit even closer to home than that.

"It's called aplastic anemia," Dr Ahn said. "It's a rare condition affecting blood cells. Luna unfortunately has a severe case. Her blood cell counts are extremely low. She needs to be hospitalised as soon as possible." Tae-eul could barely process what she was hearing. She'd heard this diagnosis before. It was the same disease her mother had died of when she was a child.

She could understand now why Luna had bolted. The news was a crushing blow.

Hyeon-min looked pale. "What's the treatment for it? How can it be cured?"

The doctor shifted in his seat. "Well, in cases like this the most effective treatment would be a bone marrow transplant, but finding a suitable donor for Luna will be difficult." He sounded reluctant to break the bad news. "Blood relatives usually provide the best chances of a match, but Luna told me she doesn't have any."

There was a breath of silence, in which Tae-eul could picture her mother's pallid face and sunken eyes. She couldn't let that happen to Luna.

"She does," Tae-eul announced. Dr Ahn and Hyeon-min both looked at her in surprise. "I mean, I do," Tae-eul corrected herself. "I have an identical sister."

The doctor's eyebrows shot up. "You do? I thought you were adopted?"

"I only just found her," Tae-eul explained, spinning a story to fit the facts.

"Wow, that's incredibly fortunate," Dr Ahn sounded stunned. "Identical twins are rare… It's the best chance of a match, though. Do you think she'd be willing to donate?"

"Yes," Tae-eul confirmed. "When can we start?"

She could feel Hyeon-min's eyes burning a hole in the side of her face, but she ignored him. This wasn't about her friend anymore. This was for Luna.

Dr Ahn looked hopeful. "We'd need to do a blood test first to see if she's a match, and then we'd schedule a round of chemotherapy to prepare you for the transfer. Hold on - let me check with the oncology department." He got up and bustled out of the room.

"What are you doing?" Hyeon-min hissed as soon as the doctor was out of sight.

"What does it look like? I'm becoming a donor."

Hyeon-min stared at her. "But why?"

"Trust me, ok? I'm the only one who can help Luna now."

"Who are you?" he whispered.

Tae-eul had seen Shin-jae at some of his best and worst moments, but she'd never seen the expression that Hyeon-min was wearing now. His gaze was so raw and full of hope, she felt like she'd just offered to save the world. "He really must love her," Tae-eul realised. It was a look she thought she'd never forget. She had to avert her eyes.

"Stop beaming at me like that," she joked weakly. "The doctor will get suspicious."

Dr Ahn returned looking excited. "There's an opening for treatment next week. If you can get your sister to come in for testing, we could start right away!"

"Great," Tae-eul smiled. "I'll convince her to come in tomorrow."

Hyeon-min was silent as they left the hospital.

"What is it?" Tae-eul nudged him.

"Did you really mean what you said back there? Are you really going to help?"

Tae-eul didn't want to make a big deal of it. She already felt guilty that she couldn't tell him the whole truth. "I will," she promised, "but it's not going to be much use unless we can find the patient. You should call her."

"I've tried," Hyeon-min groaned, "She's not picking up."

"Try again," Tae-eul urged.

Hyeon-min pulled out his phone and began dialling. A few seconds later he sighed in frustration. "Straight to voicemail."

"Give me that." Tae-eul held out her hand for the phone. Hyeon-min passed it over.

She opened up his message history with Luna and took a quick selfie. After hitting send she handed back the phone. "Done."

"What did you -" he didn't get to finish. The phone started ringing. He gave her another are-you-a-magician look and fumbled to answer it.

"Luna?" He sounded relieved. Tae-eul could hear a flood of panicked questions from the other end.

Hyeon-min wandered away as he tried to explain the situation. A while later he returned and held out the phone. "She wants to talk to you."

Tae-eul wasn't surprised. "Hello?" she answered, preparing herself for another interrogation.

"Who are you?" Luna sounded alarmed. "Why do you look like me? And what are you doing there with Hyeon-min?"

"Look, I know this is a bit overwhelming - it is for me too - but I think I can help you. I can donate bone marrow. I'm pretty sure I'm a match."

"How do you know? I've never met you before!"

"You're AB-negative, right? It's the rarest blood type."

Luna was silent on the other end of the phone.

"Come back to the hospital tomorrow. Check yourself in for treatment. I'll be there. We'll get through this, Luna." She passed the phone back to Hyeon-min, who had to spend another 15 minutes reassuring Luna that it wasn't a prank, and that there really was a stranger who looked exactly like her and happened to share her blood type.

When he got off the phone he looked exhausted, but relaxed. "She's coming back into the city tomorrow. She was staying with a friend."

Tae-eul smiled. "I'm glad I could be of some help."

Hyeon-min laughed and looked like he could hug her again. "Help? You're like a guardian angel! I owe you big time. What are you doing now? Can I buy you dinner?"

Tae-eul looked at her watch. It was almost 5:00pm. Where was the day going?

"Do you have somewhere you need to be?" Hyeon-min asked casually, though she could read between the lines.

"Don't worry, I'm not going to vanish," she reassured him. "There's just someone I was hoping to meet tonight."

"Ok, then how about a quick drink? I need to treat you to something. You've already done so much..."

Tae-eul saw Hyeon-min's pleading expression and could tell he really needed that drink. Hell, she could do with one too.

"Fine," she relented. "Just one."

They headed for the nearest bar.