Disclaimer: I don't own Pokémon. If I did Ash wouldn't make promises we know he'll never fulfill…or the writers would at least make him own up to the important ones. But I guess the odds (for example) of Max becoming a trainer and actually battling Ash are about as likely as Pikachu's Pokeball ever getting screen time.
"In the cover of your presence you hide them from the plots of men; you store them in your shelter from the strife of tongues." - Psalm 31:20
It was, as predicted, about noon when they finally arrived at Reflection Cave. Wanting to maximize time spent exploring the cave before nightfall, the group ate quickly. As they finished cleaning up lunch and were getting ready to head inside, Brock made a proposal to the group.
"So guys, I may never have been to this cave, but as a former Rock type Gym leader and Pokémon Breeder, I can tell you that cave-dwelling Pokémon can be easily frightened by large groups. In some situations this helps flush Pokémon into the open, but in most cases it just makes catching them harder. So, I think we should split up."
"You mean go by ourselves," Serena asked, fear creeping into her voice. "I'm not sure I want to go into a dark cave alone."
"Nope," Brock responded, shaking his head, "that's not what I meant. It's generally not a good idea to go into a cave by yourself, even if it is as well-traveled as this one. Too many things can go wrong. No, I was thinking we split into two groups. Ash and I go one way, you guys go the other. We meet back here at 5:00. How does that sound?"
Serena sighed in relief. "Okay, that sounds good to me. Clemont, Bonnie, mind if we take it easy and don't go in too deep?"
"Sounds fine to me Serena," Clemont replied.
Bonnie however huffed in annoyance. "Come on big brother, I want to go and see all the cool Pokémon too!"
"Now now Bonnie, let's keep Serena company. Besides, we'll have to come back through here anyways. It's on the way to Shalour City and Ash's next Gym Battle. We can do some more exploring at that point, okay?"
"Alright…" Bonnie trailed off. "Come on Serena, let's go. And you better keep up Clemont 'cos I'm not waiting for you!" With that, Bonnie took off into the cave, Serena following close behind. Sighing in exasperation, Clemont huffed after them, already panting from the effort.
"So Ash," Brock said, turning to his longtime friend, "guess it's just me, you, and Pikachu."
"Sounds cool!" Ash pumped his fist in the air. "Come on Pikachu, let's go help Brock catch a Pokémon!"
"Pika!" The electric mouse was clearly happy to be on another adventure with their old friend. Smiling, they walked into the cave.
It had only been 30 minutes and already Serena was tired of this cave. It was wet, it was dark, and all the mirrors were just plain creepy. But what she couldn't stand most of all was Clemont and Bonnie's bickering. Usually the two siblings got along well…or as well as could be expected of any brother and sister that age. But, apart from a few Woobat, they hadn't run across any Pokémon yet and Bonnie was getting irritable. Clemont, who usually had a level head and kept calm, was instead replying to Bonnie tit for tat. What's more, he had just asked them to stop for another rest break, prompting Bonnie to start ranting that a weakling like him would never find a wife.
"Well I never asked your opinion!" Irritation flooded Clemont's features. "In fact, I never asked you about marriage at all. You're the one that keeps embarrassing me by bringing it up!" He was not even bothering to hide the anger in his voice anymore.
"Well clearly you need someone to take care of you. I mean look at you…can't even go five minutes without asking to stop! It's a good thing that you aren't the one Serena's interested in taking care of because otherwise…" at this she put her hand over her mouth, shocked at what, in her anger, she had carelessly let slip. She lowered her hand from her mouth and slowly turned from Clemont to Serena, gazing at her hesitantly.
Serena had been about to intervene to try to defuse the situation, but at Bonnie's sudden pronouncement all thoughts of irritation at their conflict fled from her mind. She glanced from Bonnie to Clemont and back again, noting the looks of embarrassment and guilt on both of your faces.
With a forced calmness that was painfully evident, Serena asked, "What do you mean by that Bonnie?"
"She didn't mean anything," Clemont hurriedly interjected.
"That's right," chimed Bonnie quickly, "I didn't mean anything. I was just angry at Clemont but now things are fine, aren't they big brother?"
"Couldn't be better," Clemont agreed rapidly. "Now let's go!" Turning rapidly, both siblings began to march forward.
Serena's voice quickly put an end to the siblings' forward progress. "Not so fast you two. Who exactly am I interested in 'taking care of,' hmm?" She paused, hands on hips, a determined look on her face. The two turned around slowly and faced Serena. If possible, their expressions looked even more pained with guilt and embarrassment than before.
Suddenly Bonnie turned to Clemont, hitting him on the arm gently. "I told you we should have brought it up before, but no, you wouldn't listen to me! You're always so worried about these things Clemont and now you've gone and made things even worse!"
Clemont's temper flared. "Exactly, I told you we shouldn't say anything to avoid precisely this kind of situation. But you had to go do it anyways and now look where we are."
Bonnie's tone raised sharply. "Well if we had discussed it with her like I suggested we wouldn't be in this situation now would we?" The two siblings stared daggers at one another, neither willing to break their glare.
"Excuse me," Serena said irritably, "but you two still haven't answered my question."
"Question? What question was that?" Clemont had many talents, but acting wasn't one of them; his attempt at being obtuse wouldn't have fooled a kindergartner.
"A 'genius inventor'" at this Serena made air quotes, "couldn't possibly have forgotten something that simple already." The exasperation in her voice was impossible to miss.
Clemont sighed and began to respond, but Bonnie beat him to the punch. "You know the answer silly! It's obvious."
Her fears confirmed, panic crept into her voice. "What's obvious?"
"That you want to be Ash's wife of course!" At this Bonnie smiled brightly.
Though they both were well acquainted with Bonnie's proclivity for bluntness, Serena and Clemont were nevertheless still shocked by Bonnie's choice of words. Clemont quickly activated his Aipom arm. The robotic appendage snaked its way through the air and grabbed Bonnie from behind, lifting her up off the ground.
"Bonnie it's embarrassing enough when you do this to me!" Red tinged his cheeks. "But you can't treat our friends like this. Now I insist you apologize immediately!"
"No way big brother," she responded, struggling against her confinement. "I have nothing to apologize for. You know I'm right!"
"Bonnie…" Clemont's anger was rising again.
"Clemont stop…" Serena raised her hand. "She's right…I mean, I'm nowhere near ready for marriage of course, but I do love Ash." As she paused to collect her thoughts, Clemont lowered Bonnie back to the ground. "But is it really that obvious?"
"Of course!"
Bonnie's shout of affirmation earned her another intense look from Clemont. Adjusting his glasses, Clemont turned to Serena. "What Bonnie means is that, when considering all the evidence, it became increasingly clear to the two of us that you have strong feelings for Ash."
"What evidence?" Serena was genuinely curious just what they'd picked up on.
"Well, the biggest piece was you remembering Ash after all these years and tracking him down as soon as you realized he was in Kalos. But there are other little things as well…comments you direct specifically at him, the way you reacted when that kindergarten teacher asked him to come with her, and the way your face turns pink whenever he compliments you. Quite elementary really."
"I was hoping Brock was wrong about it being so obvious…" Serena sighed, tilting her head down, "or at least that you guys wouldn't have figured out my secret."
"Why didn't you want us to know? I thought we were friends!" Bonnie was genuinely upset by this.
"We are Bonnie! That's exactly why I didn't want you to know. I don't know, I just was worried things would be awkward for our group if you guys knew. I really like traveling with all of you and didn't want anything to mess it up. And I was also worried I'd feel more nervous around Ash if you guys knew. But now I guess you've known all along."
"Don't worry Serena," Bonnie said, "this just means now we can actually help you convince Ash to let you take care of him! Isn't that right big brother?"
Clemont shuffled his feet uncomfortably. On one hand he definitely wanted to assist Serena. She was his friend and friends helped each other out. But he was also regularly embarrassed by the well-meaning efforts of his sister to help him find a wife. He didn't want to be party to putting Ash in the same position. True, the situations weren't exactly identical; Bonnie tried to set him up with strangers, Ash and Serena were close friends. But that could heighten the embarrassment. This tension, combined with the fact that he honestly had no idea how to be a matchmaker, had driven his effort to persuade Bonnie to keep quiet. But not that it was out in the open, he didn't quite know how to respond.
Fortunately Serena intervened, "That's sweet Bonnie, and maybe I will ask for help someday. But for now, Brock has volunteered to assist me."
"That's right," said Clemont, recognition dawning, "you mentioned something about your feelings being obvious to him."
"Yeah. I was trying to be careful and find out from him if Ash has a girlfriend or a crush on someone without directly asking. But he confronted me right away, saying he already knew what I was trying to do and why. When I admitted he was right, he said he would help me."
"How's he gonna do that?" Bonnie was quite curious. She'd seen love stories play out on TV and in the movies. The heroines were always so pretty, the heroes so dashing. It's because Clemont didn't display the brash confidence of these heroes that she had long ago decided to take matters into her own hands, though as of yet she'd been unsuccessful. But now she might have the chance to see a real love story unfold before her eyes; the prospect made her giddy with excitement. "It might even help me with some ideas I can use to help Clemont," she thought.
"Well, Brock is going to tell Ash that he thinks I like him and see how Ash responds."
"But he knows you like Ash! Why not just tell him that? In fact, why not just tell him yourself?" All this dancing around seemed like a waste of time to Bonnie. If you liked someone you should just tell them; how grown-ups could make something so simple so complicated was something she would never understand.
"Because Bonnie, it's Ash that should tell me how he feels, not the other way around."
"Ah," said Clemont, realization dawning, "so you're one of those 'old-fashioned' types." At Serena's pained look, he quickly continued. "No, you misunderstand. It's true that that type of attitude is something you see much more in provincial areas like Vaniville Town than cities like Lumiose, but personally I feel the same way. That's part of the reason why," at this he turned to look at Bonnie, "I get so frustrated and embarrassed at Bonnie sometimes."
"Wow Clemont," Serena said, her expression softening, "I had no idea you felt that way."
"Pft," Bonnie pursed her lips, "sure it sounds sweet, but I know my brother. If I leave it up to him I'll be taking care of my own grandkids before he finds a wife."
"I'm not looking for a wife Bonnie!" Clemont's exasperation was clear. "Not now at least. I want to focus on my journey, on learning and growing as a trainer and an inventor. If I meet a girl that I like while we're traveling that'd be great. But it's not what's most important right now."
Before Bonnie could respond, Serena interjected. "I think you two will have to agree to disagree, or at least you aren't going to resolve this argument standing here in the middle of a cave. We're all on this journey to learn and grow together, so let's get going and meet some new Pokémon!"
At this Bonnie brightened considerably. "Yeah, let's go! And you better keep up Clemont!"
"Just remember, not one word to Ash!" Serena wanted to get this point in before they got underway.
"Of course not," said Clemont.
Serena then turned to look at Bonnie. "Bonnie?"
"I still don't get what the big deal is…" she said, trailing off. As Serena continued to stare at her, she continued, "but whatever you want Serena, I'll keep it a secret."
The group then began to walk deeper into the cave. Although the siblings did continue to bicker occasionally, the attitude of the group shifted significantly following this discussion. A calmer and more relaxed mood settled over them and stayed with them for the rest of their time together in Reflection Cave.
Considering Bonnie's search for a wife for Clemont and that neither of the siblings seem to approach Ash-level density when it comes to romance, Serena's interest in Ash is obvious enough that in a realistic world they clearly would have picked up on Serena's feelings. However with anime you never know. For the purposes of this story I assumed that they have noticed and put forth a reasonable interpretation of why they haven't said or done anything wrapped within (what I hope is) a comedic and in-character exchange.