Have you already completed your transfer to Balmung? If not, there's a chance that "Fate Testarossa" will be taken and you'll have to name-change anyway. And if you wanted to, you could always double-check and even ask if someone would be willing to make a character with that name so you could get a free name change. Don't feel like you have to change your character's appearance or anything like that in order to fit in; you're free to do whatever you want. But the name directly lifted from an anime character's is likely where people are drawing the line.
