Just think about those inescapable "sexy" nicknames. The related Sixtus is not a huge improvement.

West African naming tradition dictated that children were named for their time of birth or birth order — Nsia would have been given to a sixth-born baby girl.

Used by the ancient Romans to distinguish a sixth daughter from her sisters of the same name. The first three letters make it pretty much unusable today.

The name of several popes and saints, Sixtus is certainly unusual but would have trouble making it in the modern world outside the Vatican. Even worse is its brother Sextus. Try making it through seventh grade with that name.