Raw is available as an upgrade path for blacksmith Andre of Astora after he is given the Large Ember. Uniquely for an ascension path, Raw requires only Large Titanite Shards as upgrade materials, as well as a standard weapon +5 and the requisite souls.
Raw increases the base damage of a weapon, while reducing its stat scaling from Strength and Dexterity. As its name suggests, it gives the weapon jagged edges, making it more dangerous but also more unwieldy.
It is a unique upgrade path in that it does not allow a second tier of ascension. It essentially functions as a way for players to maximize their attack power early on in the game, with Raw +5 weapons generally more powerful than Normal +10 weapons. However, Normal +15 weapons are always stronger than their Raw +5 counterparts.