A Charm Bangle will not work in the Via Infinito, so don't bother. But, you should have won a Charm Bangle from one of the LeBlanc trio fights, unless you sold it or something.

Another tactic against the Black Element is to a Songstress ability called Magical Masque, which nullifies all magic attacks against your party. To get this you have to defeat the maxed out Experiment in the Djose Temple, which gives you Magical Dances, vol. 2.