Prologue
We start of in Music Land. It's an Island in the Sky with 5 worlds, but for right now we're focusing on one of them, Music Town (World 1).
It all started after Mario & Luigi had saved Peach again, and again, and again, and needed another vacation so Peach thought of the perfect place for them to go, Music Land. It was the perfect choice, it's a place with open fields a soothing music so she asked Toad to go their and build them and himself a cabin for them to stay in so he did and they took the SS Brass The Lakitus of Music Land built for transportation between The Mushroom Kingdom, Music Land, and the worlds in Music Land which they lend to Toad so they can go there and after all that, they were off to Music land.
After settling in, Toad took a walk to see what was around while Mario and Luigi stayed in their cabin. While looking around, he saw someone break into Truffle Towers. It was Waluigi so Toad went to see what he was doing he overheard that he was going to use the Music keys to take over The Mushroom Kingdom by sending them away and keeping them away until chaos descend down onto Music Land and spread across The Mushroom Kingdom and then him and anyone else who would join him will rule over the remains. Waluigi then sent to 3 of the 4 Music Keys to different places in Music land. Toad then knew that he needed some help getting them back and he knew just who to ask, The Mario Bros.