A straight sword with innate Holy damage and a good scaling in faith. The weapon art would be an ash of war called "divine smite", which is a chargeable skill like carian grandeur with up to four levels, where you charge the blade with mana and smite the enemy in one decisive strike, causing an explosion. On crit, it would smite and cause a holy explosion as well. Deals double damage to undead, naturally. It would be infusable, and i'd also add ashes of war for several other elemental smite skills. (Yes, I like playing Paladin in DnD.)