As seribii Ash knew Serena as a kid, this is a little one shot for them. Disclaimer, I don't own Pokémon.
Alexa asked Ash, "So, do you want to come to Kalos? There are new Pokémon and places to explore." Ash replied, "Yeah, I promised a childhood friend I'd come by and maybe travel with her, I haven't seen her since I was seven."
Ash called out, "Serena, where are you?" A small blond girl replied, "I don't want to go, I don't want to leave my best friend!" Ash said, "How about this, I'll write every day and one day I'll be able to come and visit you, maybe we can even travel together, how does that sound." Serena replied, "Ok, but promise me that you'll visit someday." He said, "I promise!"
Ash explained, "I traveled far and wide so I'm going to finally go to her hometown, don't worry I know were her hometown is. I told her this and I rarely ever break my promises. I'm excited to see her after so long!" Alexa said, "Well, I'm heading to Vanville town, is that her hometown?" Ash nodded, he replied, "Let's get going, we can't be late for the plane or boat or whatever!" Alexa chuckled, "Get your bag and Pikachu and let's get going to the plane." By the time she was done talking he was ready, Delia called out, "Don't forget your underwear! And please tell Serena I said hi!" Ash got embarrassed as they left and he yelled, "Mom! Ok, bye" Delia said to herself, "Ash, you are so much like your father, please be safe." During the ride Alexa noticed how nervous Ash was and asked, "So, how'd you and Serena meet?" Ash replied, "It's a long story."
Delia called out, "Ash, our new neighbors are here." Ash came downstairs and the woman with blond hair and green eyes said, "Our daughter Serena has vanished, have you seen her?" Delia replied, "No, I'm sorry, you can get lost in the forest nearby but don't worry the Pokémon won't hurt her." Ash went outside and said, "I'll find her, no one knows that forest like me!" He ran off, he climbed a tree and tried to spot her, he called out, "Serena, don't be scared my name is Ash, my dad is a friend of your parents." A small blond girl asked, "Why are you here? I was playing didn't mommy and daddy hear me say that?" He replied, "Not sure, but maybe playing here isn't a good idea, weedle live here and they're mean. Come on after we tell our parents we can go to my favorite spot to play." A man who looked like Ash asked, "Ash, what are you doing here?" Ash replied, "This is Serena, she wandered over here by accident. Can we play in our secret spot dad?" His dad said, "Sure, but make sure Charizard is near you at all times." He took Serena through a place where the trees looked like a tunnel and led her to a place with tall bumpy hills, Serena asked, "How is this place fun Ash?" Ash replied, "This is where I train to become a great Pokémon master. It's also where dad and I play tag. Tag you're it." She laughed, "No fair Ash Ketchum, I wasn't ready."
They landed on the ground, Ash went outside to the top of the steps, jumped and yelled, "Finally!" He thought he saw someone, Alexa asked, "What is it?" They got down the steps and Ash replied, "Nothing, I just thought I saw Serena." Someone poked him and said, "Tag, you're it." He looked around and found a girl with long blond hair several feet from him, he ran and laughed, "Serena!" He got to her and said, "No fair, I didn't expect you Serena!" Serena replied, "Oh, you didn't expect your best friend to be waiting for you for years and start acting all giddy when his best friend calls and says he'll come without his girlfriends." He shouted, "I don't have a girlfriend!" Serena chuckled, "Yeah, and I'm a little kid." Ash said, "You are a little kid, so are you going to travel with me or not?" Serena replied, "Duh Ash, of course I am, and I didn't bring a bike so you won't barbeque it." Ash said, "Those were accidents! Besides you don't have to travel with me if you're scared." Serena replied, "I'm not scared Ash Ketchum! I will be the very best, like no one ever was!" Ash yelled, "Hey, that's my line, and no I'll be the very best, like no one ever was, it sounds better coming from me!" Serena laughed and asked, "You coming slow poke?" Ash called out, "No fair Serena, you got a head start, see you later Alexa." The two friends ran off, into their future.
And that is probably not going to happen but oh well, please review.