Mt. Silver, a place with some of the strongest Pokémon you can capture, only open to trainers of admirable skill. Professor Oak, as you know, will allow you to travel here once you beat the Elite Four. Because he sees how well you battle, how well you treat your Pokémon, he allows you to travel to Mt. Silver to take on its challenges. But is this truly the only reason? Surely there are other trainers than you that are deserving of this reward, right? So, why you, of all trainers? Why are you so special?
Because you are the only one who can set him free. Other than the Pokémon Center that is located there, there are virtually no other people. There is one, though. Located at the tippy-top of Mt. Silver, alone. You should know him well. You were him once, after all.
Red is a former ‘apprentice’ of Professor Oak, receiving his pokedex many years before you start your journey. After his travels, he, like you now, gained access to Mt. Silver. After training here, he climbed to the top of Mt. Silver…and isolated himself from the rest of the world, training in solitude, losing contact with anyone and everyone who he considered worthwhile.
He didn't call his mother, Professor Oak, or even his rival, Blue. None of them had any clue what had happened to the boy; any calls they sent were rejected or ignored. After awhile, they stopped calling. But Professor Oak, curious as to what had happened to the boy, climbed up to Mt. Silver, reaching its peak. It had been well over a few years since he had lost contact with Red.
What he saw sent a wave of terror down his body.
He saw Red, or rather, Red’s lifeless body, in a corner of the chamber. When Professor Oak checked, it was cold. He’d been dead for awhile now. He shuddered; why had it suddenly become so cold in the room…? He turned around, jumping backwards in surprise.
He saw Red, sitting on a rock across the room, staring at him with a blank expression. His amber eyes were dull, and red lines had formed under his eyes. He had been crying. With this, the Oak turned to the body, to Red, to the body, to Red. How…how could they both be Red? Red continued to stare at him, and Oak could only stare back in shock and terror. He watched as Red removed something from around his waist, and Oak recognized it as a pokeball. It looked aged, though, cracked in places. Red, ever so silent, mouthed two words to the professor as he gestured toward the pokeball.
The professor backed away a little, but stopped as he saw Red was not going to react to anything he did. “How…” the professor stammered. “How can I help you…Red?” Once again, Red gestured toward the pokeball, and Oak finally understood. “I’ll…I’ll do everything I can for you, Red.” Red smiled at him, silently fading until the professor could no longer see him.
Over the next several years, the professor constantly searched for a trainer, one worthy of helping the poor spirit of Red. But, no matter how hard he searched…no one, not one trainer, could do the deed. Anyone who did dare to climb Mt. Silver fled at the sight of Red’s spirit. The professor was getting desperate and, in one last attempt, he consulted Lance of the Elite Four for help. Lance himself couldn’t help, but he and Oak decided this:
Before any trainer could be allowed entrance to Mt. Silver, they must prove themselves worthy by defeating the Elite Four. This became the rule, and so, they waited for the trainer that would be the one. For a long time, this trainer did not come, and they had begun to lose hope…
Until, that is, you came along. During his time in Johto, the professor visited a childhood friend of his, Mr. Pokémon, who had offered to help the professor with his dilemma. When you met Professor Oak, he saw the potential in you as a trainer…and offered you the pokedex.
He kept track of you, of your growth as a person and a trainer, up until your final battle in the Elite Four, where you proved your worth as a trainer. Because of this, the professor gave you access to Mt. Silver, hoping you to be the one that could finally free Red. He didn't explain to you the plan, only hoping that you could handle it on your own.
When you finally make your way to the top of Mt. Silver, Red, as he normally would, is isolated on Mt. Silver. He is honestly surprised when he sees you, for he has not had any challengers in a long time. You walk up to him without fear, and, wordlessly, he challenges you to a battle. You accept, and the two of you engage in a battle powerful enough to shake the heavens.
When the deed is done and you have won the battle, Red does not speak. He wordlessly returns his last Pokémon. Afterwards, he is there for a brief instant, before disappearing from your view, and he is no longer there. When you look, the body is gone as well. You stare at the place where he disappeared and, though you couldn't be sure, you thought you had seen a faint smile forming on Red’s face upon his defeat. Red had one last unspoken reply for you, his savior, who had freed him from the world at last.