Duo Destinies

Unlock and equip Mystic Spearhand. You get the vocation from Sigurd - you meet him during the story, then track him down again (he heads to Dragonsbreath Tower) to have it unlocked, after which you equip it at any Vocation Guild. Sigurd is also who hands over the Mystic Spearhand maister teaching for 203958047, so it's worth doing his thread thoroughly.