There's not a lot to do in a small town like Inaba.
On the one hand, the town is fairly safe and quiet (those, umm, murders are a new development). However, on the other hand, that stillness can be boring, so you end up making your own fun.
Y'know, hobbies! Arts and crafts, sports, TV, video games, stuff like that!
For you specifically, it was music. One day when you were in the big city nearby with your family, you passed by a music shop and were instantly enthralled with the guitar on display.
A beautiful, Blue Vintage Silvertone electric guitar.
You've heard it's a fairly decent and affordable brand, if not a bit cheap.
But you did not care at the time. That guitar was yours goddamnit.
After working your ass off and saving up the money, you managed to purchase the guitar and finally call it your own.
It sits in your room and you play it regularly. Sure, you're not the best, but you can play your favorites. ((Can you tell I play guitar?))
Yosuke had begged Rise to perform at Junes to save his dad's job a couple days ago.
Rise, ever the advantages idol, agreed under the condition that everyone in the investigation team performed with her.
Cue whacky hijinks.
Marie had volunteered as one of the guitarists during that event, using one of Yosuke's guitars, and she seemed to have liked playing the instrument.
Knowing you're the only other person with a guitar, Marie came to your house one day.
Marie: "...Hey. You're the one with that blue... Gritard? I want to play it."
No tact whatsoever. But regardless, you let her in and into your room.
And for a while, she just... Plays guitar. Playing the Velvet Room theme, the song she performed at Junes, and some random notes and strings here and there.
For a moment, you sit and listen to the strings vibrate through the amp.
Marie: "...My fingers don't hurt as much as last time."