How to go about using charlotte as Xander's pair-up

[Spectraman]

So i am not going to lvl up charlotte. How would guys so I should go about using her as xander's guard stance? When should I promote her for the stat boosts and all?

[Thor Odinson]

Promote her asap if you're not planning to level her. Stats do not affect pairup bonuses--only class, support rank, and personal bonuses do.

[eclipse]

Promote to 'zerker, watch things die. Xander doesn't need the Hero's Def.