An ancestral side to the Barbarian would fit. The Germanic and Norse "barbarians" revered their anscestors, to call upon your anscestors in time of need would fit if they based the Barbarian class upon them. It could take the form of a spirit mask or a physical mask as some has suggested.
They, just like tribal groups aronud the globe, had shaman. To add a shamanistic side to the Barbarian class would be interesting.