01- Mario
It was yet another peaceful day in the Mushroom Kingdom. The toads ran and played, the princess was safe in her castle, and Mario happily slept in his little house. It hadn't been long since Bowser's latest defeat, but the event happened so often that the kingdom was able to go back to life as normal very quickly.
The day was off to a good start as Mario got up and went through his morning routine. Curiously, Luigi was nowhere to be found, but the red brother gave it little thought as he headed out the door, heading to Peach's castle. Though there likely wouldn't be another crisis anytime soon, he liked going to the castle from time to time in order to make sure the princess was safe.
As he ran toward his destination however, he noticed a small shape running towards him very quickly. Before he knew what to do, a small, yellow creature tackled him, knocking him to the ground. The rodent dropped an envelope, squeaked cutely, then ran off again. Not knowing what to make of the situation at all, he sat up and opened the letter, hoping to gain some insight on the situation.
"Mario,
You have been personally invited to participate in a tournament comprised of the universe's twelve greatest fighters. Your prowess in defeating the evil king Bowser so many times makes you a perfect qualifier to fight for the title of 'Champion of the Universe'! You will have a month of preparation before a representative comes to get you. The only prerequisites are: You may only fight on foot, and you may not tell anybody else about the tournament. Best of luck!
-Hand"
With a grin, the plumber sprang up and ran off to the castle
Peach's castle, several hours later:
Mario was standing next to a toad scientist, inspecting some experimental new power-ups. Though instructed not to, Mario had immediately told the princess the situation that he was in, and she immediately sent him to see her scientists.
"So, as you can see here," the toad began in his high-pitched voice, "we currently have two primary experiments we've been working on. This fire flower and this cape feather have been engineered to stay active, even after you take a few hits. With a few more tests, they'll be able to last you about as long as the tournament. They'll likely wear off once you get back though, so don't get used to them!!"
With a firm thumbs-up from Mario, he headed off to train for the tourney.
AN: There we go, chapter one out of the way! For those wondering where Pikachu fits in to this, just wait until his own chapter and all will make sense. Also, I really struggled to think up an in-universe reason for Mario's specials, so I decided on the toad scientist thing for simplicity. And come one, who doesn't think toads in tiny labcoats is totally adorable? Leave criticism down below! Until next chapter!!