Not all arcane warriors wield a single heavy blade. Some prefer lighter fare. The black blades, cognizant of varying fighting styles, shape themselves into sundry forms—sometimes splitting in two.
Light Weapons: A black blade, as detailed in Ultimate Magic, is a one-handed slashing weapon, rapier, or swordcane. This rule expands the selection to include light piercing or slashing weapons. A GM can fine-tune this expanded selection as necessary to ensure that all possible weapons are, in fact, blades.
Twin Weapons: Alternatively, any class that could receive a black blade may instead choose twin light weapons from the available options. This choice is permanent until such a time as the black blades might need replacement (such as in the event that they're destroyed).
Enhancement Bonuses: If a character selects twin black blades, he must split the enhancement bonus granted by his class levels between the twins. If the enhancement bonus is +1, one of the twins has a +1 bonus and the other is treated as a masterwork weapon. It is still a magical item, and has a minor evocation aura, but it does not bypass DR/magic and it must be given a +1 bonus before it is enchanted with any weapon special abilities. If a character has twin black blades, he must allocate at least a +1 bonus to each of the blades at the earliest opportunity (usually level 5). Each twin can have an effective individual bonus of up to +10 at any time. Keep track of each blade's enhancement bonus and special qualities separately.
Somatic Components: A spellcaster wielding twin black blades does not need a free hand to cast spells with a somatic component; he can use one of his blades to perform the appropriate gestures.
Oneness and Separation: Though the twins are two weapons for the purposes of spells like magic weapon or abilities like blade thirst, the twins are still considered one item, and both must be wielded for the purposes of the black blade's telepathy and alertness abilities. The blades share one set of ability scores, languages, and skills—essentially, they are the same single character. Twin black blades, if separated from each other by more than 120 feet, instantly gain a new purpose: to reunite. A forlorn black blade will attempt to dominate (see: Items against Characters) anyone who comes across it and force them to aid it in its quest. During their time apart, both twins lose all abilities based on their arcane pools. If one of the twins is destroyed, the other becomes a nonmagical masterwork weapon and loses all its abilities: the black blade's soul is dead.