Character name is...Viva Reverie
Viva Reverie is the ponysona of Viva "IMMATOONLINK" Reverie. While her creator is male, she is female. He doesn't like the design of stallions in My Little Pony, so he opted to be represented by a mare.
Yeah I don't think she has a backstory. She's just the face of the channel.
Behind the scenes Edit
Yeah her rainbow plus cutie mark is cause she's a gay doctor. Totally. Not making that up.