SPOILERS
i don't recall ning jun destroying his crystal? before the fight siena and ning jun were in the cave trying to find the labratory and they found it and the wizards set the sieger children free. then it cuts back to kain and erika after they talk with the elder and have the fight with the wizards. piero talks to erika and erika still doesn't agree so kain and erika fight him. perhaps i should do more exploring in the cave to find the scene with ning jun nullifying the crystal?