Mewtwo.
The strongest psychic in the world, and arguably the strongest pokemon to exist, at least known to man. And he is currently...
"Here you are, Zekrom. One letter from Groudon, one from Victini and... three from Reshiram?"
"Wouldn't surprise me if she's arguing about why truth is more important than ideals, and all her reasoning couldn't fit in one or two letters..."
...Delivering letters?
Let's go back a few days to see what in the world has happened...
Flashback
Mewtwo stood atop a building, watching the humans running about. At times, he was envious of them. They never stop to ponder upon their purpose in the world. As long as they fulfill their desires, nothing else really matters. If only my life was so simple...
Created by Team Rocket for the purpose of becoming the ultimate weapon, Mewtwo escaped and intended to destroy the world, and remake it with clones of pokemon, free of the 'infestation' called humans and weak 'normal' pokemon. A human had made him see the error in his ways, and he found himself lost: he thought it to be his purpose to remake the world, but now...
Sometimes, I wish the answer could just appear out of nowhere, but it's never that easy...
"Really, now?"
Hmm?! "Who said that?!" Mewtwo frantically looked around, both with his physical eyes as well as his mental powers, but there was nothing within a three kilometer radius that was paying attention to him. Was it just my imagination...?
"No, I can assure you I'm real."
"Where are you then?! SHOW YOURSELF!"
"I want to, but there're too many eyes around here."
"Is that so? Then, shall we meet up in the sky, or are you not capable of flight?"
Mewtwo heard a rumbling laughter that somewhat unnverved him. "I assure you, that won't be an issue." As the voice finished, Mewtwo found himself teleported by another power, and wound up above the clouds. Remembering his bout with Genesect, he was quick to erect a barrier to protect himself from the cold.
What in the world... it should be impossible to cause another being to teleport without physical contact!
"It's only impossible because you believe so... and due to your lack of understanding regarding the laws of the universe, but that's unimportant right now. Look behind you."
Mewtwo did as he was told, and saw a large, white horse, with a golden wheel attached to it's abdomen. He had the knowledge of all pokemon known to man, yet this being wasn't familiar to him.
"It would be rather strange if I -was- known to you, seeing as even myths about me are believed to be nothing more than fairy tales. I am known as Arceus, and the few humans who are confident in my existence think of me as a god. While it's true that I did create the universe and almost everything in it, I do not seek reverence."
"I-I see... and for what reason have you sought me out, Arceus?"
Arceus merely tilted it's head slightly. "Did you not desire an answer? While I can't give you a purpose in life, as that's wholy up to you, I can at least give you something to do, if you wish for it."
"Alright, you've got me interested. What do you want me to do?"
Arceus nodded, and the two of them teleported. As the light faded, Mewtwo found himself in a grand hall, made out of what he believed to be marble. He had never seen something so beautiful and awe-inspiring.
"This is the Hall of Origins. My home, as well as yours. And other legends, occasionally. Most tend to live on Earth, and that makes contact... difficult, aside from the times we have meetings."
"And that's what my job will entail, I take it?"
Arceus gave of a feeling that it smiled at his query. "You catch on quick. Yes, your ability to teleport may be inferior to my own*, but that can be changed with some training. Also, unlike me, you have a lot of free time on your hands, no?"
"Yes."
"Also, don't think you're obligated to do this in case you accept: if you so desire, you're free to quit at any time. And at the same time, you're free to keep going for however long you wish."
Mewtwo nodded at the info. "Sounds good. Then, how am I supposed to relay information?"
Mewtwo got stumped when Arceus showed him a plain letter. "Seriously? If you're using human inventions, why not simply use telephones?"
"Because they can be intercepted. A letter carried by the strongest psychic in the world? Not so much."
Mewtwo sighed. "Alright, I get it. When do I begin?"
Arceus nodded and pointed with on of his hooves at the letter in Mewtwo's paw. "Might as well begin with whatever is at hand, yes? You're free to go to whatever legend in any order, as long as you make sure to visit each one at least once a day."
"Even Mew?" Mewtwo shuddered slightly. He hadn't seen Mew since their battle at New Island. While he was certain the pink cat didn't hold a grudge against him, it would still be awkward.
Arceus just stared at him blankly, as if saying 'Do you even need to ask?'
"Alright, alright, I'm going..."
*Yes yes, I know Arceus can't learn teleport, but he's the closest thing to a god! Cut me some slack, alright?