"So, how are we going to find this Celebi then?" Meowth asked. Everyone looked around the room, hoping one of them had a plan. However this awkwardness was shattered when a water shuriken appeared out of nowhere and slammed into Meowth. Gary hurried to Meowth's side. "Meowth, are you alright?" he asked the Pokémon concerned. "Yeah… I mightn't look it but I can take a hit," Meowth grunted and shook the stars in front of his eyes away. Then a Greninja appeared directly in front of Meowth with a cut attack ready to strike the Pokémon. Serena immediately recognised the Pokémon. This was Ash's Pokémon, there was no doubt in her mind. "Greninja… stop! Meowth is on our side," she exclaimed and threw herself between Greninja's cut and Meowth. Greninja's eyes narrowed and shook its head. "Gren Greninja!" it replied angrily to Serena. "Meowth translate for us," Gary muttered to Meowth. Meowth glanced at Gary but obliged. "You don't understand," Meowth translated, matching Greninja's tone. "Then explain everything to me," Serena coaxed gently. Greninja looked at Meowth but let the cut attack disappear. "Gren greninja nin gren ja ja," Greninja began. Meowth swallowed but translated as Gary had asked. "That Meowth is the reason Ash is gone."
(This next bit is similar to how Misty explained what happened only from Greninja's point of view)
Greninja had heard the explosion and ran as fast as possible to where it had come from. It had to run half way across the forest to get there. When it got there it saw Ash running after Team Rocket's balloon shouting for them to return Pikachu. Greninja caught up to Ash and with one look knew that Ash wanted them to go through their transformation. Their feelings synced and a surge of energy went through Greninja as the water enveloped it. It could feel Ash's desire to get Pikachu back and also Ash's deep rage that Team Rocket had stolen his friend yet again. They were also the reason that Serena was missing. Greninja and Ash merged fully. As one they threw the water shuriken with all their might. Together they felt their frustration when the attack missed and together they heard Misty call out her warning. Ash stopped in time. Greninja knew it couldn't stop though and jumped after the balloon. He heard Ash's command and began its Aerial Ace attack. However when it saw the female Team Rocket member pull out a rocket launcher, he knew he had to dodge. He used the power of the Aerial Ace attack to change direction mid-jump and landed behind Ash. Only then did Ash and Greninja realise what was going to happen.
The rocket hit the cliff and Greninja felt the vibrations itself and through its connection with Ash. Greninja felt Ash's fear as he fell. He didn't notice Bayleef run to the edge and fire its vine whip as it threw its tongue out into the dust cloud desperately trying to catch Ash. Their connection strengthened as their fear climbed together. Then Greninja felt through Ash the rocks falling around him. Greninja felt Ash's pain as one crushed his arm and the numerous bumps and bruises as Ash tumbled down the cliff face. And finally it felt Ash hit his head, hard. The next thing it knew, it was waking up a few feet away from the ledge. Bayleef was murmuring incoherently to itself and Misty was on her knees staring at the edge, still in shock. Greninja heard people gathering around the rumble below them. However it knew that looking was useless. It had felt Ash die. It knew its trainer was gone. At first it despaired but then it grew angry. It longed to avenge its trainer and fulfil Ash's dying wish. That night when everyone wasn't looking it ran away and started its search for Pikachu.
Greninja finished its explanation and glared furiously at Meowth as Meowth finished translating what Greninja said. The room was silent. Gary was the first to recover. "Why did you come back now?" he asked softly. Greninja moved its gaze to Gary for a split second and then returned it to Meowth. "Gren gren ja ja," it muttered. Meowth's eye widened. "You did?!" he exclaimed. "Gren nin ja greninja ja ja… gren gren ja ja ninja," Greninja replied haughtily. Meowth was silent, clearly admiring what Greninja had said. "Meowth, want to clue us in?" Gary prompted. Meowth snapped out of its trance. "Greninja said that it found Pikachu. It followed a couple of Team Rocket guys with a Celebi to a facility up in the mountains nearby," Meowth informed Gary excitedly. "How did you see those thieves? You had to be close by before that… why?" Tracey realised and broke the silence. Greninja turned to Tracey. "Gren nin nin ja greninja," it replied calmly. "It comes back this time every year," Meowth translated. Everyone understood, Greninja was back in Pallet Town to remember Ash and probably its vow to its trainer's memory.
"Greninja, could you lead us to that facility?" Gary asked gently. Greninja turned to Gary and gave a curt nod. Meowth smiled and made a move to leave the room to get things ready for their hike. Greninja immediately slashed its cut attack in front of Meowth, preventing it from leaving. It clearly didn't trust Meowth. Gary held his hands up to calm the situation. "Greninja, Meowth isn't working for Team Rocket anymore. Meowth tried to rescue Pikachu and has helped me greatly in my research," Gary tried to convince Greninja. "Besides we'll need his help to get into Team Rocket's facility," Gary added seeing that Greninja hadn't believed him. Greninja looked at Gary and then stood back and motioned to Meowth that it could leave. Gary couldn't help but marvel at how much Greninja was like Ash. It had gone off on its own to protect everyone, just like Ash would have done. It had been searching for Pikachu all this time, something that Gary knew Ash would have done. Ash had always been very proud and dead set against accepting help especially from other he considered enemies or rivals. Greninja was acting the same way at this precise moment. Within an hour they were ready to leave.
I just want to say that I don't know if what I've said happened when Greninja and Ash "merged" is right, I made that up. I kind of wanted to get as close as possible to experiencing what the event had been like for Ash without doing it that way. I know that Ash feels Greninja's pain in the anime when they're like that, so I thought that it was probably the same the other way around.
Anyway… until the next chapter.