Phillip
Making his way in the tennis court, who's to say Leon got lost or he was actually interested in having a tennis match? It was mostly with his Pokémon when he did these sport activities since most of the people he know are out busy somewhere. Entering the area, though, he was surprised to see a girl was there already and he wondered if she could play by herself or he can challenge her.

But it's obvious what he was going to do.

Walking up to the individual, he hopes he doesn't scare her and says a loud, "Hey there!" It's because of the bangs covering over her face that Leon assumed it'll be hard for her to see anything at all. Since she was shorter he had to lean over her a bit. "Mind having a opponent?" Leon isn't a superstar like some would assume. He only watched how tennis played rather than playing it himself. But it's just beating the ball over the net, back and forth, right? It sounded easy!
Walter
Rhea did not jolt from the voice; rather, she turned around right as the man spoke, getting a bit of telepathic communication from her Pokemon to alert her before she got spooked. She moved her bangs a little bit, looking up to the man and realizing it was the champion; it made her turn away, a bit embarrassed, realizing that she was comparable to him since she was invited.

Rhea gave a small pat to her Musharna before lifting her communication device, going to the typing section. After some quick typing, the Rotom voice spoke through. 'That's fine. I don't really know how to play though, so please be patient.' She then paused for a moment, looking up at Leon and down at her device. 'Sorry.' She added to the text-to-speech. 'I use this to talk instead. While we play, if you don't mind, Musharna can tell you what I'm saying. I ask this because I don't want to intrude on your thoughts without permission.'
Phillip
At first Leon was was shocked. He did expect the girl to talk, and if she did, it'll be a quiet voice. Not saying he was going to stereotype her like that, but at first glance (and watching how she hit that ball) she probably didn't go out often, or wasn't social at all. Alright! That made Leon more pumped up to help her try. "At least I can understand you!" Of course, Rotom were usually useful in everything now. He pats her communication device as a good job. "I never played either so we're in this together. I'm just going off by what I saw on TV." 

Standing back straight up, he puts his hands on his hips to appear as grandiose as he usually is. "Oh! By the way, I'm Leon! From Galar! What's your name? And who's your friend over here?" He motioned to the Musharna nearby, glancing at them a bit before returning his eyes to the girl in front of him. "Really? That sounds wicked cool! I don't mind that at all!" He meant about the telepathy. "So long as it's not static, alright? I think I have enough of that in my head, aheh!" He can make fun of himself every now and then!
Beth
'To answer the question you have not asked, she's mute. That is why she isn't talking. Though, if she did speak, it would be very difficult from her condition.' A voice played in Leon's head, sort of that of a gentle young woman's voice. Musharna simply had to get that across before anything continued, but Rhea would not know of the communication unless mentioned.
Walter
She nodded to him as he explained he was about on the same skill level, only knowing what TV showed. So, she looked back down at her device and began typing away. 'Yes, I've heard of you, Leon. I'm Rhea. And this is my Musharna, who helps me to train. She's always with me.'

Just in case it wasn't quite loud enough, or perhaps he wasn't paying attention, she flipped the device around to show what she typed anyways. Now he could clearly see the amazing organization of the device, with buttons for many categories so she could talk about anything she wanted to.
Phillip
"Nice to meet you, Rhea! And just Musharna, right?" He dares pat the Pokémon. Leon was known to be touchy-feely, especially with Pokémon he just met. It's a weird greet in a way—especially when they might attack him upon first contact. He never saw Musharna before—or at least haven't been near one before. Seeing it up close, he's almost getting sleepy somehow. And he's usually the peppy one! "You've heard of me? Really?" He says with not much awe. He expected as much that anyone would recognize just the name "Leon from Galar!"

Once the device was turned to him, Leon leaned close once again to scrutinize the many buttons. "Whoa, this is- what is it?" He was lost, in the mind, at first. It was so much to him, he didn't know where to focus first. When his eyes settled on one thing, it moved to another, then another, but he couldn't understand it at all. Wanting to not appear like an idiot, he nods his head. "This is some complex keyboard!" Standing back up, once again, he reassured, "That's why you can't be carrying it around as we play. Go ahead with the telepathy!"

Walking to the other side of the court, Leon saw a bunch of rackets lined up in brackets for their choosing. Picking one up, he flipped it and tested it in his hands. Even if he's fresh at this sport, each had something in common: to win. Leon was determined to appear "The natural" Once again when picking something up for the first time. Next, he got the tennis ball, and he tested its bounce on the clay flooring. "I'll tell you something now, Rhea. I don't lose battles. So prepare yourself." Looking back at the girl, his eyes held something different, the competitive spirit inside of him burning instead of the everyday Leon.
Walter
She nodded to him, pausing to watch Leon get confused by her device, before flipping it back towards herself. 'I don't find it complicated since I'm used to it. But anyways, yes, I know you.' She typed, waiting to listen and deleting it. After all, the board only had so much space for text.

'I went to Galar for some time to train and saw you everywhere. Now I see you here. It feels weird, not in a bad way.' She then finished, taking the strap off of her shoulder and putting the device in a safe location.
Beth
'She doesn't want to break the device, of course.' The voice played through both their heads. To Rhea it was there just to understand the conversation in real time. 

'.... Also, she's clarifying that this isn't a battle to her. It's a game. She doesn't see a need to compete.' The Musharna telepathically continued, moving over between the nets like a referee of some sort. She was out of the way and could watch them both... And she could be prepared in case a ball went flying, out of the area or into someone's face.
Phillip
Leon rubs the back of his neck almost shyly, before getting on a good stance and twisting at his hips to display the famous Charizard pose. "I expect nothing less. I've been the unbeatable champion for a decade now." He boasts this as if Rhea didn't know—when she made it apparent that she did. Well, it was a good excuse to show off his pose anyhow. "Tell you what, I can give you my League card after this match! As commemoration." Bouncing the ball, he got in position. Left bottom corner of the court, right? He steps up to the spot, and throws his cape to the side. 

"But competition makes us perform better! It's like getting a rival for your Pokémon journey—the next time you meet, you want to show off your skills that you've learned since last time. I can have you as my rival here on the tennis court, Rhea! Even if we begin as newbies together, I'll show you that I have the potential to make it-" And he throws the ball in the air before slicing down on it with his racket, sending it quickly to Rhea with an almost accurate direction. There was a little curve in it, though.
Walter
Rhea simply tilted her head at the rant this guy was going on, watching the cape go flying off to the side before focusing again. With her opinions on fame, she found all of this as odd and a bit confusing. And boy, the league cards really threw her off.

With the game already seeming to start, she let out a sharp exhale, hurrying over and hitting the ball. With her luck, the ball actually went over the net and back to Leon, focusing on her thoughts again.
Beth
'Well, for one, not to disrupt the game, but she has no clue what a League Card is. Aside from that, she figured it would be neat to try to battle you with Pokémon over tennis. In tennis, she just wants to learn and have fun.' The Pokémon carried the message through, hovering from side to side whilst watching them.