There was no denying the changes in the three of them once they were back home. Sora, Kairi, and Riku were completely different people from the three children who used to dream of worlds beyond their tiny island. Tidus, Wakka, and Selphie had noticed the changes too, how Sora had come to understand things maybe a little too much, how Riku had shadows behind his eyes, and how Kairi seemed to worry about them more than she ever had. But as the weeks and months passed, things slowly settled into a state closer to normal. Kairi started ordering the boys around again, and they would respond with a joking, "Yes, Princess," to which she would laugh. Riku and Sora resumed their old rivalries, racing each other on the children's island—but Sora won more often than he used to. One day, in the middle of a game of blitzball, Tidus asked them what the other worlds were like. They'd paused for a minute, Sora looking at Riku before he responded.
"There was a lot of darkness," he explained. "Sometimes, it seemed like it would destroy everything. But still, there was always a light shining deep inside the shadows."
From time to time, Sora's friends from his journeys came for one reason or another, whether it was a Heartless infestation that had somehow thrived, or just a visit to an old friend. During those times, Sora, Donald, and Goofy would share stories about their adventures and about their lives in the present. Wakka and Tidus listened to each story with extremely childlike enthusiasm, making Selphie and Kairi laugh. But then Sora and Kairi would cast wayward glances toward Riku, who always seemed like he was trying to escape at those times.
"How is Mickey doing?" he finally asked one day, to everyone's amazement. Goofy explained that the King of Disney Castle was doing great, and everything suddenly seemed to be back to normal.
But things couldn't ever fully go back to normal; they were too deeply scarred by the darkness for that. Sometime after they'd come back, Riku and Sora returned to the secret place with Kairi. There, all three of them took sharp rocks and carved images of themselves into the cave walls: Kairi wearing a crown, Riku holding a sword and wearing a cloak, and Sora carrying the Keyblade. Then Sora had painstakingly drawn all of his friends from his adventures and placed them within the door to Kingdom Hearts. Riku and Kairi had watched him the whole time, helping out whenever they knew a person they wanted to draw. When it was finished, they closed the secret place and never looked back.
Personally, things weren't easy on them either. Three weeks in a row, Kairi woke in the middle of the night from nightmares of half-forgotten memories. Sometimes they were of Hollow Bastion when she was little, before she came to the Destiny Islands. Sometimes, they were of the Heartless attacking Traverse Town while Yuffie, Leon, and Aerith tried to protect her during her stay there. And sometimes, they were of Sora stabbing a Keyblade through his own chest to release her heart while he became a Heartless, and Riku falling into darkness to save her, letting Ansem take him over. She never spoke with anyone about it—not even to Selphie, who had become her best friend while Sora and Riku were gone. But Sora and Riku noticed, and one night as they lay out on the beach and stared at the stars, they mentioned her tiredness and distraction.
"It's just a few nightmares," she answered. "I'll be fine. I promise." And she was. The very next night, the nightmares stopped. That short conversation had been enough.
Riku had accepted the darkness in his heart with Mickey's help, but he still kept in mind that Ansem could take control once again. Even though he'd mostly gotten over it, he still felt violated by Ansem's taking over his body. Ansem had aged his body during his time in control, warping his features with the powers of darkness. Sometimes, Riku was afraid that as he grew up, he'd start looking more and more like Ansem, so he did whatever he could to spare his friends the pain of seeing him grow into that. He made sure his hair never grew past shoulder length, and he stayed inside reading to avoid getting a deep tan. For several weeks, he'd neglected his friends and immersed himself in his studies. It was only when Kairi and Sora became worried about his health that he realized the irony: In trying to avoid becoming Ansem physically, he was starting to become like him mentally. That made him shut his books and challenge Sora to another race. He won.
And for the longest time, it seemed like Sora had been the one who had changed the least. Although he won more bouts with Riku and had found the courage to confess his feelings to Kairi, he was still very similar to the fourteen-year-old who had no idea where his destiny lay. He still lost to Tidus and Wakka in their games, and Goofy and Donald joked around and picked on him when they visited.
But then a Heartless ship crashed on their island. It too had survived despite the sealing of Kingdom Hearts and all other measures Sora and King Mickey had taken to defeat them. Before anyone else could do anything, Sora called upon his Keyblade and quickly dispatched all of the Heartless, allowing no one to fall prey to them. It was then that everyone truly realized that he was the Keyblade Master, and that perhaps was what had made him change most of all.
One week after that battle, Sora stood barefoot in the water, feeling the waves lap up against his ankles. A half-eaten ice cream bar hung loosely from his mouth as he stared out into the horizon. Only a year ago, Riku had declared that they would sail out to find the other worlds. And now they had been to them, and things would never be the same.
"Hey, Sora!" Kairi called. He waved her over. "What are you doing?"
"Nothing much," he answered, taking the ice cream out of his mouth. "Just thinking about how much things have changed." She nodded and took his hand. "Sometimes, I wish things could go back to the way they were, but I'd never trade my experiences for anything."
"Same here," Riku agreed, walking over. He hardly squinted at the sun as he looked to where the sea and the sky met. "I think we needed to go through all that. It's just part of growing up." They looked at him in surprise. This was hardly the way they'd expect him to describe their experiences. "We're not children anymore. Maybe it's for the best."
"We have learned more in the other worlds than we ever could here," Kairi admitted. "About light, darkness, love, loss…" She went silent for a minute, remembering how afraid she'd been that she'd lost her two best friends, and how afraid she was that she was going to forget them. "We know more now, and we've seen everything we've ever dreamed of. Maybe things didn't turn out the way we planned, but it still did us a lot of good. We're more than we ever thought we could be. You're heroes. I'm a princess. Just knowing that is amazing."
"Yeah," Sora replied, closing his eyes and reaching deep within his heart. There lay the power of the Keyblade, almost humming in tune with his heartbeat. Also there were images of every friend he'd made along his journey, bound to him with threads of fate. They could never be taken away from him. Maybe he, Riku, and Kairi had changed over the past two years, but in their hearts, they would always be the same. And that was all that mattered.
Standard disclaimer applies: I do not own Kingdom Hearts or any of the Disney or Square Enix characters. This has a slight AU edge since I haven't yet played Kingdom Hearts II, but I try to keep it just to Kingdom Hearts I references.