The idea is from MingmingK.
Not quite sure if that's what you wanted, so sorry.
Next MiTzu if I can finish in time.

 Nayeon was bewildered. She watched the youngest girl acting cute in front of her and asking to pat her head as the approval that she did well. Tzuyu wasn’t the type to do so which made the other wonder whether it was a prank or someone just controlled Tzuyu’s mind. She still did as the taller girl asked and stared at her happily skipping to the other side of the hall where they had photo-shoot.

 Jihyo and Jeongyeon who sat near didn’t even pay attention to the whole situation, both stuck in the phones, but the oldest member didn’t really know what to do. It was happening for the whole month now and she was starting to get worried about Tzuyu’s health as well as a mental state. It was fun at first and Nayeon would lie if she says she didn’t enjoy all of it, but it was happening for too long.

 She glanced to the other side where Tzuyu spoke with Chaeyoung. She was still the same – laughing and shining with her bright smile and dimple, she still playfully hit her friend when the smaller one said something and still was Tzuyu they all knew. But Nayeon felt that something changed in the way they communicated with each other. She was surprised to notice the long serious stares in her direction or the way Tzuyu cared for her, more than usual and better than Nayeon expected.

 This all also happened so suddenly that she had no time to think of her reaction. And it couldn’t be the fact that she entrusted her feeling fully to the group. She was still trying to hold sadness under her blanket and show a smile when it was lifted the other day. So Nayeon was getting confused day by day instead.

 ***

 Tzuyu didn’t know where it came from. She watched Nayeon practising her part with dance instructor, but all she got focused on were those moves and Nayeon’s face. She was literally hypnotized while others preferred to look at the phones during a quick break. The confusion grew in her as she had no idea what was the strange throbbing feeling inside her chest. It was pushing her to be with Nayeon as much as possible and it was even harder to resist. She was shocked by herself when she started to show affection to her unnie, obviously scaring the living out of her. But it was happening so naturally and it caused her so much happiness that the younger was even afraid of herself.

 She wasn’t stupid to understand that it was the affection of some kind, but it sounded impossible to be this interested in the member of the same group. She never viewed Nayeon more than just an unnie and what was happening to her now?

 One more thing that surprised her the most was the fact of how she reacted on Nayeon watching other girls or boys. She felt at peace as long as it was girls from Twice, but when Nayeon ran to other members of groups to greet them and talk, Tzuyu’s heart was squeezing and it painfully hurt her lungs.

 In hard time, she usually talked to Jihyo and they would find the solution in the end or at least calm each other. But as Jihyo was Nayeon’s closest friend, Tzuyu felt threatened to approach the leader. Instead, she found a talk buddy in Chaeyoung, who knew about this stuff not too much but was willing to make Tzuyu feel comfortable in talking. They never used names but the smaller girl was still able to give some advice. She could see how scared and worried Tzuyu was and it was a rear sight for her to witness. But if her friend needed her, she would always be there.

 Chaeyoung’s ideas were great, but Tzuyu doubted them. She couldn’t possibly check if Nayeon liked her – the oldest unnie liked everyone and in Tzuyu’s opinion referred to everyone on the same terms. Nor she couldn’t just confess and make herself embarrassed if Nayeon would freak out of her actions. So the questions were still present.

 ***

 Nayeon swore the last few weeks Tzuyu was stuck by her side and now she avoided her as skillfully as she could. It was frustrating. They were having the days off and the younger was out from the morning, hanging out with friends. Nayeon occupied her bed in thoughts listening to the sounds of game Mina played near.

 The puzzles weren’t clicking in her head. One day Tzuyu was ready to spend the whole day clinging to Nayeon and gift her with hugs and attention, the other she was nowhere to be seen and would rather hide in the corner of the room to be as far as possible. Nayeon didn’t know what kind of game they were playing, but it was only getting her frustrated and worried.

 She knew that the youngest usually spoke with Jihyo about her problems, but when she tried to get any information, Jihyo said that Tzuyu hasn’t come to her in a while. Nayeon wanted to just go away, struggling to find answers on her own, but the leader was worried now as well, so she just pulled Nayeon in the empty space to chat.

 “What happened?”
 “I don’t know. Did you notice the fact that Tzuyu had mood swings or something these days?”
 “Mood swings?”

 Jihyo had no idea. She tried to remember any of it, but in her memories, the youngest was her adorable fluffy self the whole week.

 “Well, she’s like being all lovely with me and then just turns her back at me.”

 Nayeon looked so dumbfounded that it made the other one laugh very hard, but the older girl wasn’t joking at all. She frowned, watching her friend rolling on the floor.

 “Isn’t she always like this with you?”
 “No!” She was getting angry. “Tzuyu is always sweet. She would never avoid me like that.”

 Jihyo stopped, examining the older girl before leaning on the wall.

 “Fine. What did you do then?”
 “I don’t know.”

 The conversation didn’t help even for a bit, but Nayeon knew there was a problem and it has to be dealt with.

 ***

 Chaeyoung was staring at her for a few minutes now, annoying Tzuyu already. They just happened to both prepare to go out and eat outside, when Nayeon appeared out of nowhere. She stopped Tzuyu by grabbing her hand and gently pulling the younger one.

 “Can we talk?”

 Watching them gave the smaller girl a weird feeling. It was obvious that Tzuyu wanted to escape the conversation and Nayeon looked as serious as ever. Chaeyoung stood there, not able to take anyone’s side as she looked in Tzuyu’s hopeful eyes.

 “Actually, Nayeon-unnie, we had booked the table and we’re being late, so maybe after?”

 Nayeon glare was scary and both youngest felt uncomfortable as the other one was visibly controlling herself. Still, she let them be and informed that she would be waiting.

 Now Chaeyoung waited for an explanation while their order was preparing. Tzuyu tried to avoid the questions at first, thinking that her friend might forget it, but as soon as the waiter went away she met with interrogating stare in her direction.

 “Okay. What?”
 “What was that?”
 “I just didn’t want to talk. That’s it.”
 “No, you’re never being this ridiculous. What the real reason?”

 Tzuyu sighed, messing her hair and lowering gaze on the floor.

 “Remember, I told you about someone I like…”
 “So it’s Nayeon-unnie?”
 “I think it is.”

 Tzuyu was sure about her feelings for a couple of weeks now. There was no way her heart was beating this rapidly over other people presence and this was only Nayeon that could trap her attention completely. But since she didn’t feel that attraction from the other girl’s side, she thought that it was one-sided and it must stop before she would hurt herself and destroy everything. She swore to herself that Nayeon would never find out and she even thought of the excuse to tell every time the older one would ask what the matter. So, she was sure she was mentally prepared for the conversation, even if she was worried as never before.

 ***

 Nayeon was angry about everything that happened to be in her eyesight. She hit the blanket as her legs made her stood up and she was pacing in the room again.

 This was impossible that Tzuyu hated her. She did absolutely nothing to deserve this. And her actions were pretty confusing to call it to hate. Which could only mean the opposite and knowing the opposite, Nayeon thought she might be crazy to even think of that. No way in the Earth Tzuyu was in love with her. It must be a sisterly love, right? Friendly love. But who would be embarrassed by this love? Tzuyu was absolutely fine with showing affection to any other member of the group, especially without cameras. But what the heck was with Nayeon?

 As she paced and hit the wardrobe hard, she gasped. This can’t be true. She can’t make her hopes high and got disappointed again. She loved Tzuyu, not like a sister or friend and it was long gone. At least, she hoped it was.

 The girls came back after a while and Nayeon jumped out of the room to meet them. She didn’t care about Chaeyoung’s words. The only person she needed now was Tzuyu. She took the girl’s hand and forcefully pulled her in the room, locking the door to not be disturbed. Tzuyu looked little standing in front of her and Nayeon felt bad for acting so rude.

 “Tzuyu-ya, we need to talk. Did something happen? You’re acting weird.”
 “No, unnie. I was just not feeling well.”
 “No, Tzuyu. Tell me. I’m stressing myself out because you avoiding me all the time.”
 “It’s not like…”
 “Tell me.”

 It was hard to deal with Nayeon when she was in such a bad mood. Her eyes were concentrated on the taller one and Tzuyu felt trapped and helpless. She didn’t know how to say it and she was sure her lie would be discovered and cause more troubles. But how would Nayeon react scared her the most? Still, if the older girl would avoid her for the rest of her life, at least, Tzuyu would know that she tried.

 “Unnie, I think I fell in love with you.”

 Nayeon didn’t know whether the thunder just sounded in the room, but she was deaf for a second here. Her heart raced and she froze, not knowing how to react. She loved Tzuyu from the start, but younger one showed no interest, so she stuffed this feeling deep inside her and it was working until now.

 “Why only now?”
 “Because it came unexpectedly. I’m sorry.”
 “Don’t be.”
 “No, I’m sorry, I couldn’t notice it when you were interested as well.”

 Nayeon lifted head up.

 “You knew?”
 “It was obvious. I was so scared of it and tried to run away every time.”
 “Will you run away now?”
 “It depends on your answer.”

 Nayeon smiled, pulling the girl closer for a hug and nuzzling into her neck, felling the younger one’s heart jumping out of emotions.

 “Then don’t. Surround me with kisses and affection and I’m yours.”