So actually written as prologues it myself;) I would try to help yes, but a prologue has a thousand faces, it can be a passage from the story, something that has happened before, the idea of the character, etc. From there you would need more precise ago details ^^
And the characteristics should not just copy, unless they are free, there is, after all copyright and stuff like that, and there is but your story, so you have to look at what you value ... I think it would be important at Vocaloids definitely hair color, eye color and music direction and possibly hairstyle or special characteristics, otherwise the usual halt, such as name, age, hobbies, personality, friends etc.
I hope I could help a bit ^ ~ ^ I stand on issues, drafting, Beta reading or so happy to help :)