Sorry if May is OOC, I've never seen the Hoenn series. I have heard a lot about it on the Internet, and I actually have a good idea on who May is. But tell me if I do something wrong, I'm happy to accept advice. Also, when the storyline starts and flashback ends, May is almost 16, Ash is 16, Misty is 16, and Brock is 21.

May met Ash when she was 10 years old. She fell in love with him at first sight, despite that his Pikachu electrocuted her bike. She wanted to help him become a Pokémon trainer, dreaming that one day they'd be more than friends...

But it wasn't easy. May thought she was going to be all alone with Ash until his friend from Kanto, Brock, came. She did like Brock, but it took a long time to get used to the fact her and Ash wouldn't be alone. Plus May wasn't even sure if Ash had feelings for her. His other friend from Kanto, Misty, seemed pretty close to him. She didn't know Ash had never dated a girl, though. Also it's not exactly too easy to admit you're in love with your best friend. Ash would probably have freaked out, thought May was nuts, and never talked to her again. But there was also a chance he'd feel the same way. After all, May's Bulbasaur fell in love with Ash's Bulbasaur, and that type of thing only happens when the trainers do. All those times she wanted to tell him, she never got to. She either got interrupted, got too nervous, or lost all hope.

Ash Ketchum had gone through Kanto, Johto, and then went to Hoenn. He met May and never thought he'd ever met a girl better than her. But Ash isn't the type to be all lovey-dovey, and he tended not tell anyone about it, so he just played cool. No one suspected a thing, except for that time where Oscar and Andi called the two a couple. And when James from Team Rocket called May his 'girl'. Ash liked everything about May. Her friendliness, intelligence, soft heart, beautiful looks, everything about her. He wondered what could make her even better. Eventually he realized nothing could. When Ash went through Sinnoh and Unova, he missed her and wish she could stay the whole time with him. But he could always look at his half of the ribbon they split in half, since they both earned it. It brought him good luck, happiness, and motivation. Ash never parted with the ribbon, and his friends in Unova had no clue why. Sometimes Ash actually wished he could ditch them and visit May, Misty, and Brock. Especially May.

After Ash lost the Unova Pokémon tournament, he decided to go to Hoenn. Ash knew his way to Petalsburg City, May's hometown. He found the gym she now ran with her little brother, Max.
"Finally, after all these years," he said to himself before entering May's gym.
His hands started shaking, but he opened the door despite his anxiety.
A familiar voice called out, "Who's there?" It was May! She came to the door a couple minutes later, looking shocked.
"Ash! Did you win the tournament?" she asked.
"No, I didn't, but I came here to see you," Ash told her.
"Aw, coming all the way to Hoenn just to see me! I would've done that for you, too. But I still run this place, Dad gave it to me."
"Cool, you're a gym leader! But why can't you just give the gym to Max?" Ash questioned.
"He's not even old enough to be a regular trainer! His birthday is almost here, luckily. I can teach him everything I know and this place will be his. Max said he'd like that." May explained.
"So, want to go surprise Misty & Brock back in Kanto?" Ash asked.
"Okay! I'd love to meet Misty, you've told me so much about her. Plus Brock will be glad to see us again."

So they traveled to Kanto by boat. When the two arrived in Cerulean City, May was amazed.
"Wow, Misty must run a tight ship. She has an awesome gym!" May gaped at the building. Ash knocked on the front doors, and saw it open. Misty was the one who opened it. She gasped at the sight of Ash.
"You're back from Unova?" Misty asked.
"Yes, but I didn't win the tournament. Oh, Misty, this is May. May, this is Misty." Ash introduced them to each other. May & Misty hugged each other.
"I'm so glad I get to meet you!" Misty told May.
"Me too!" May squealed. Once Ash, Misty, & May went back inside, Brock came in.
"Ash, May, tell us when you're coming next time!" Brock joked.
"I decided to surprise you all, and I really wanted for May & Misty to meet." Ash said. The reason he wanted to introduce May to Misty is because if they became best friends and her & Ash dated, Misty would be glad for her. And they wanted to meet anyways, so why not?
"So, your 16th birthday is approaching, May?" Misty asked.
"Yes, it is. And my little brother's. We were born on the same day in different years." May said. "You guys are all invited to the party, by the way. It's going to be the best Sweet 16 ever! Imagine, it'll be so romantic and beautiful! There can be ladies choice dancing, and I could dance with-" she stopped herself before she could say Ash.
"May, secret meeting. Come into the hall." Misty said. May knew what she wanted to know. "Who were you going to say?" she asked. Exactly what May thought.
"Promise you won't tell anyone, okay? And you can give me a secret of yours to me in return." May asked, a little unsure she should do this. Misty nodded. "Okay, Misty, it's-" (she lowered her voice) "-Ash."
"In return, here's my secret. My secret crush is Brock. I've loved him since I was 10, but I always thought I was crazy for it." Misty whispered.
"It's okay, Mist. I've loved Ash since I was 10 also, and he was my best friend. That felt just as weird. You might as well join the club." May joked. Ash & Brock called them back, and ran back to them.
"So you planning your party yet, May?" Brock asked.
"Yep. I'll have it here. It'll be coed-" Brock cheered.
"Anyways, we'll be able to do karaoke, and I'll even do something special for a certain person." May told him.
"Sounds cute." Brock said.
"Yep, it will be. I'm not telling you now who the certain someone is now, unless you keep it between us." May said.
"I have to tell you guys something, too. Let May say what she needs to first, I can wait. It seems personal, so I'll go upstairs and play with the water Pokémon here." Ash told his friends. Neither May & Ash knew what was going on in each other's minds.

"So, tell me now, May. I never knew you had a crush!" Brock said, feeling like he was being let in on a conspiracy.
"If you tell, I'll kill you and hide the body..." May told him with a murderous tone.
"Okay, I won't, May! That's not the type of person I am!" Brock said, fear evident in his voice.
"Okay.. It's Ash." A big moment of silence passed until Brock spoke again.
"Wow. So, why are you telling me this?" Brock inquired.
"I need a favor from you and Misty. At my Sweet 16, I said there'd be a ladies-choice dance. One of the reasons I did that is so I could get Ash to dance with me. I have another reason, but I prefer not to share this information. Don't even ask, Brock, you're not getting it out of me. Anyways, when I said we are doing karaoke, I decided my Sweet 16 would be the day I could tell Ash my feelings. In song. I don't know if I'd have the courage to do it." May explained.
"Why don't you think you'd have the courage to do it? It sounds like the type of thing you'd be perfectly comfortable doing." Brock said.
"Well, I don't like singing in front of others. Plus Ash will be in the crowd. For all we know, I could mess up. And when I get nervous, I throw up." May explained, like she was teaching a Kindergartener addition. He understood.
"May, sing for us." Misty begged.
"Do it, May, we think you'd be good at it." Brock added. May started blushing, but gave in.

Cause I'm all about him, him, him
And he's all about me, me, me
And we don't give a dang, dang, dang about nobody

"May, that was good! You have nothing to be afraid of." Misty encouraged her. Ash came in all of a sudden.
"You guys done yet?" Ash questioned. May knew he wanted to talk to Misty & Brock now, so she left.

"Can you guys help me surprise May at her Sweet 16? I want to ask her out in the most romantic way possible." Ash said. Misty & Brock looked at each other for a couple of seconds, then Brock answered him. "Okay, we'll help. What's your plan?"