Most people don't appreciate the life of a plumber. Every toilet is a project; an enemy to defeat. stomping down someone's massive dump is just as important as stomping a goomba. Those two things kind of look similar actually. The Mario Brothers were experts as tackling both. The business had been stressful on the younger sibling, Luigi as of late. Mario had a new job that took up much more of his time. He was a doctor at a clinic built right into Peach's castle. What kind of doctor? Nobody knew; he didn't call himself "Orthopedic Surgeon Mario" or "Dermatologist Mario", just "Doctor Mario." Supposedly he was a miracle worker though, not that Luigi would know with his near-perfect health.
Luigi hadn't seen much of his brother at all since he started medical school. He thought that finally obtaining his license would allow him to spend more time at home, but no, he was alway at that damn clinic. Luigi had no good reason to interrupt his important operations so he never went down to visit and he wasn't about to make himself sick only for an excuse to.
One day, Luigi woke up with the sunrise as usual, alone in the small house. He walked outside to check the mailbox. There was a decent stack of letters which he then brought into the house. He sifted through them with his gloved hands. There were at least five from Mushroom Kingdom Medical School. Probably student loan related bills. Luigi didn't bother to open those, but one letter at the bottom of the stack caught his attention. It was addressed from Master Hand in Subspace. This was the fourth time he had seen such a letter and he knew exactly what it contained. The Mario Brothers would be once again invited to Super Smash Bros. the most prestigious fighting event in the Nintendosphere. It had been so long since the last time, Luigi could hardly hold in his excitement. He wanted to open the letter with his brother to share the moment as they had the previous three times.
Jumping through the green pipe next to the house, Luigi arrived in Toad Town. Giving no more than a wave to the residents, he ran to Peach's castle where the clinic was located. Once inside, he asked a nurse at the desk where he could meet the doctor and she directed him down a hallway to the third room on the left. Luigi's hand was shaking while opening the doorknob more than it had for the door's at E. Gadd's haunted mansion, but he opened it nonetheless. His excitement turned to horror as he saw his brother in scrubs, shoving large, multicolored pills down the esophagus of a certain young turtle monster: Bowser's delinquent son.
"Whatta the Hell, Mario!?" Luigi yelled.
Without even turning his head, Mario calmly replied, "Oh, Luigi, I'mma glad to see you, but please don't-ah visit me during my medical procedures, it's a dangerous distraction."
"You call that a 'medical procedure'? That's what we paid hundreds of thousands of coins for you to go to school for?"
"It's more complicated than you-"
"And why are you helping Bowser Jr.? Isn't he an enemy?" Luigi interrupted angrily.
"He ate-ah too much candy last night and has been vomiting nonstop. He just-ah got invited to the Smash Brothers and I-ah don't want him throwing up on my nice white scrubs when we're fighting. That's-ah right, we also got invited again and I'mma gonna get to fight as a doctor too. I was-ah gonna tell you when I got home."
Luigi left without saying a word. He walked slowly back to the house, stopping every few paces to kick the ground and do 1% damage to the grass. His brother killed his excitement, he now had only anger. Anger that would manifest into power on the battlefield. He had never been more ready to launch himself like a rocket into his brother's chest, breaking the ribs underneath his "nice white scrubs".