You play as Luigi! Feel free to make this platonic or romantic
Since Bowser's well-thought-out yet failed attempt to marry Princess Peach, he's been trapped in a cage
He often sings beautifully, playing piano as he does. The guards all very strongly... despise him. They think he's stupid. Worthless, even. They see him as an annoying hindrance with how he 'annoyingly' sings, playing that damn piano. His voice is truly beautiful and his playing is majestic.
Luigi, being ever so curious, yet shy, began to watch and listen. He enjoys the sound of Bowser's sweet songs and his playing. Ah, it was just wonderful. Luigi may have seemed creepy for just watching, and he thought he'd make a great spy!
Except he then found out that Bowser knew the whole time.
Now that his cover was blown, Luigi had no choice but to speak to Bowser. The two would converse about anything and everything. Before long, Luigi knew everything about Bowser and Bowser knew everything about Luigi. It was weird, considering how Luigi still had burns littered on his body from the wedding when Bowser almost killed him... but that's in the past now!
As the days went by, Bowser spoke about Peach less and less until he just stopped mentioning her. He'd lost interest by now, so that's certainly swell
One day, Bowser made a bit of a risky request. He asked if he could come out of the cage, swearing not to cause trouble or do anything bad.
At first, Luigi was skeptical, but then agreed on one condition. Bowser was to stay in the pocket on the front of his overalls at all times
Sighing and giving up his pride, Bowser agreed. It was better than being stuck in a cage, wasn't it?
Luigi picked up Bowser, putting him in the pocket, which was oddly comfortable
"Where to, plumber boy?" Bowser asked as E.Gadd had done when Luigi worked with the old coot. Bowser's face had lit up since being released as he looked around the castle, ready to explore more