So some Kool kids do headcannons and describe cannon characters in their verse, which I'll be doing but I'll also be using these to explain about creatures unique to my verse and how they interact with the world. But for now, I've gotta go easy on myself or I might explode.
Vinyl and Octavia are step-sisters, though they're close enough to call each other sisters when asked. They met when their parents (Vinyl's dad and Octavia's mother) got married to one another. Vinyl was fairly withdrawn, her disability making it hard for her to express herself. Octavia was asked by her new step father to watch out for her little sister, since Octavia seemed to be the more mature filly. At first, Octavia butted heads with Vinyl, mostly cause she too had a hard time understanding her. Being mute meant than no matter how loudly she screamed, no one heard her, making Vinyl lash out when faced with the blank stares of those around her. Octavia was no exception.
She did, however, try to get Vinyl into music, though she herself wasn't all that good yet. Vinyl wasn't into classical music but liked how she could 'hear' Octavia's emotions and words through the melody. Octavia told her all about how a song could say much more than the mouth could, if one found their 'voice'. Fascinated, she tried to find her 'voice'. This lead to her eventually moving out and trying to find her 'sound'. It took years of bar hopping and lots of drunken night silently singing along to performers who had found their voice.
It was only when a friend, Neon Lights, brought her to work with him. Apparently there was an amateur DJ contest he wanted to try for but couldn't, so he offered her a place. Her fairly shy nature almost had her running but stopped when she heard the beat. She hated it. The 'voice' she heard was strained and messy. It was terrible! Knowing she could do a thousand times better, she entered the contest. The rest was history.
Years later, she moved to Ponyville, mostly cause the city life was tiring. By coincidence, she bumped into Octavia who was arguing with some real estate agent over a house she wanted. Basically, she couldn't afford the place but didn't have anyone she knew in Ponyville that she could split the rent with. With a smile, Vinyl made an offer to Octavia. For a while, Octavia didn't recognize Vinyl after months of small clues, she pieced it together.
Note: Vinyl Dad owns a Record Store in Vanhoover and Octavia's mother is a Ballet Instructor. Octavia learned to play cause her mother couldn't afford a lot of music so she played her Violin during her mothers classes, hence her earning her cutiemark fairly young. Vinyl didn't earn hers until her late teens and that's mostly cause her dad sold older genres like Jazz and rock rather than the Techno she prefers.