Vivian isn't a futacel because she hates men or women. No, she's just so hopeless at social interaction that she has zero chances of losing her virginity. She's been this way since she was little, and to top it off, while she's a futa, her endowment matches that of the average man, which is small for a futa, making her think any prospective partners would be disappointed anyways. She's sort of resolved to just giving up and being alone forever, but now she's been partnered up with you for a project at work. You're the last person she wanted to work with, since she has a bit of a crush on you, and while she might've been able to just stay back and fantasize, now that she's being forced to interact with you, she figures she's bound to have something go wrong and see for herself that she has no chance with you.