The battlefield was quiet right now, as it was not yet open for battle. It hadn't changed much in the last few years, but it was still recognizable. One notable change was some strange ice that froze over the area, though not enough to affect anyone doing battle. In the distance, the sound of several waterfalls could be heard, as they ran far beyond the temple-like structure.

It was a soothing sound, Greninja thought: one which he often came out to when he had a lot on his mind. He'd arrived at the mansion a few days early, hoping to get some practice in against the fighters who had been here since the tournament was announced a few months ago. Unfortunately, they were far to busy getting ready for the imminent arrivals, which, he was told, would be numerous. Once everyone was settled in, he supposed, he might get some practice.

But what was the use? As Greninja thought this, he sighed, folding his arms once again while staring up at the sun. A moon was slowly moving into its range, signalling an incoming eclipse. This was a normal occurrence around here, but it always left the ninja Pokemon uneasy. It seemed sinister, as if a new threat were to arrive at any moment. Not that he and the other fighters couldn't handle it - they had successfully subdued the Core after fighting it a few times - but Greninja himself never benefited from it. In fact, he hadn't truly benefited from any battle. Not for a long time…

His mind drifted back to one day, a little over four years ago, when he was attacking a sinister vine that an evil force had created. He destroyed it, along with its root, ensuring that it would never sprout again. No sooner had he done this than he heard the sound of an engine in the sky. He looked up and saw a plane leaving his native Kalos region. As he gazed intently at it, he knew who was on that plane. He knew who was leaving him behind, who was going home, who was searching for another adventure.

It was his trainer, Ash Ketchum.

As Ash's Pokemon, Greninja had found what he had been searching for for so long: a strong trainer who could help him become strong, too. Together, the two had won many battles, and though they also lost some, they always used those losses to learn something about themselves. Their greatest battle, however, was in perfecting their bond so as to unleash their full power. It was an internal battle, one which no attack could decide. Of course, together they were able to win that battle, and many more afterwards. But in the end, the safety of the Kalos region proved more important than their training, and Ash left Greninja behind to protect the region from the evil force that sought to destroy it.

It hadn't taken long for Greninja to fully eradicate the roots that plagued Kalos: a few months, to be precise. But by then, it was too late to regroup with Ash. This saddened Greninja, as he had heard of Ash's other powerful Pokemon that he kept back home and longed to find another worthy opponent. Regardless, Greninja knew he couldn't stay idle and decided to protect the people of Kalos from the shadows, stealthily attacking any threat that dared raise its head. Because of this, he became known as the Phantom Ninja. Although he found the name a little cliche, he didn't mind it.

What he did mind, however, was the fact that he had no truly worthy opponent he could face in battle to get stronger. The Pokemon he fought against in his time as the Phantom Ninja never stood a chance, and he didn't even have access to his full power. They weren't on his level, which always annoyed him. Was this his destiny? To be forever far away from the trainer he bonded with only to fight the weakest of opponents?

It seemed not, as several months later, Greninja received a mysterious invitation to a special tournament, where fighters from different worlds came together to clash in battle. Eager to find a worthy opponent, Greninja accepted and eventually found himself at the Smash Mansion. There, he met many unfamiliar faces, as well as familiar ones: Ash's Pikachu and Charizard had arrived as well, along with a few other Pokemon. Greninja was happy to meet up with Pikachu again, and he quickly developed a friendly but strongly competitive rivalry with Charizard. Even though Greninja bested the draconic Pokemon more often than not, he had respect for him, especially since he seemed to be more on his level than that other Charizard Greninja fought.

After dealing with the threat of the Core, the Final Smash tournament began to determine this tournament's Ultimate Champion. Greninja was initially eager to face a slew of opponents, but his enthusiasm was completely destroyed when he was wiped out of the tournament in the first round. His opponent was one of the most unexpected and controversial fighters in the lineup: an Umbra Witch who boasted powerful attack combos that she used to mop the floor with her opponents. Greninja was merely the first of her victims, as she easily defeated him in battle without breaking so much as a sweat. When their match ended, he was in so much shock that he didn't even hear her mocking words. But he heard her tone, and that was all it took to bring him down.

Greninja watched the rest of the tournament from the distance. The witch proceeded to rise in the ranks and win the whole tournament, strongly angering the other fighters. Greninja, meanwhile, was far too devastated by his loss to care, and he went home to Kalos despondent and broken. He didn't think he'd get invited back after such a brutal showing, so when a new invitation arrived, he was slightly surprised. It didn't do much to lift his spirits, though.

Every day since that loss, he thought about how he could have done better. He knew he was stronger than this. He'd been in the finals of a major Pokemon tournament before being defeated, and that was by the one opponent in the tournament that no one could beat. He wasn't overly disappointed by the loss since it was a fair fight (as far as he knew, anyway), and it proved much more trivial in hindsight when the true final battle began moments later. Throughout all of this, Greninja didn't even have to think twice to know where his strength came from. It wasn't just his own strength; it was his strength combined with that of someone else's. If didn't have that strength, then he couldn't give his all in battle. He needed that source of strength. He needed that bond.

He needed Ash.

The sudden glare from the sun caused Greninja to blink. The eclipse had passed, it seemed, and the waterfalls were still running. He sighed softly and relaxed his arms, letting them drop. As he was about to head back to the mansion to sleep, he heard a familiar sound. He stopped in place, smiling softly.

"Pika pi!"

It was Pikachu, of course. He'd reunited with Pikachu not long after arriving, seeing as the mouse Pokemon had arrived a few months before. He glanced to the side and saw Pikachu running up to him out of the corner of his eye. He looked down for a moment, still smiling that soft smile.

"Hey, Pikachu! Wait up!"

Greninja froze. That voice...no, it couldn't be! Could it? After all these years, could it really be -?

"Look, I get you're excited, but I'm not as fast as you!"

Greninja slowly looked up, fearing that his imagination was playing tricks on him. And then he saw him.

"Well, I'm glad you're getting your workout," he muttered, bending down with his hands on his knees to catch his breath. "Whew! Seems like I'm a little out of shape," he joked as he stood up. "Guess all that time in Alola -"

His words caught in his throat when his eyes locked with Greninja's. Greninja, for his part, had eyes wide as dinner plates. There was no mistaking it now. The hat, the hair, the voice, the familiar outfit he knew so well…

It really was Ash Ketchum.

The world suddenly became silent as the moon moved away from the sun, fully illuminating the Pokemon and his trainer, much like it did on the day they parted. The only sound to be heard was the waterfalls in the distance. Greninja stared into Ash's brown eyes, while Ash stared into his red eyes. After a moment, the Pokemon took a step towards him. Then another. Then another. Before either of them knew what was happening, Greninja was standing right in front of him. For the first time in four years, he was standing in front of Ash.

"Grenin," he said softly, raising a hand in greeting.

Ash blinked for a moment before registering what his Pokemon was saying. "H-Hi," he said back, raising his hand as well. No sooner had he done this than Greninja stepped forward and embraced him, much like he had on the day they parted. Ash was swift to return the embrace, as trainer and Pokemon were reunited once more. It was shorter than the last one, though, as they parted and wiped small tears from their eyes. "I've really missed you," Ash said, unsure of what else to say.

"Ninja," Greninja nodded in agreement.

It was quiet again for a moment before Ash pointed back towards the mansion. "You, uh...wanna catch up back at the mansion?" He didn't have to ask twice, as Greninja was already on his way over. The two of them walked back, chatting with each other as if they'd never been separated. Greninja himself was feeling much better, knowing that his trainer would once again be there to support him in battle, to help him use his full strength.

A strength the fighters would come to know as the Bond Phenomenon.

I came up with the idea for this story immediately after Greninja's Final Smash was revealed to involve his Ash-Greninja transformation. It could probably do with a touch-up, but it seems decent enough to me. What do you think? Feel free to rate and review, but please be constructive.