Titantic weapon(s) have 5 size increase from the standard weapon size (medium).
It is meant to be welded by only large creatures, and is welded at DIS by any creature smaller than COLOSSAL, and cannot be welded by a creature 2 sizes smaller.
Each weapon size increased from the standard weapon size damage dice is increased by 1.
If a player wishes their weapon to be made this way, it often nonstandard size for the forge so it would require a special forge.