There exists abilities that are specifically tuned to certain individuals or clans. One of these strange abilities is known as blood-bending, which is the power to turn an individuals' blood against them. Blood bending can be used in several ways to fulfill various purposes. A user can bend an individual's blood in order to control their movements and actions from a distance. It can be used to draw a victims blood through the pores in their skin in order to manufacture physical manifestations of objects instantaneously. This can be specifically used to form weapons in battle, such as swords, sickels, projectiles, etc. Finally, a user can draw out a persons' blood and absorb it into their own supply, healing wounds and restoring their life force. While blood bending is a poerful technique, its effectiveness can vary between the different blood types. Certain blood types are blood types are barely malleable, and would remain mostly unaffected by a skilled blood bender. Others are moderately effective, with a user being able to control their movements to some extent, and create brittle and easily shatterable weapons from them. Some can be very affected by a blood bender, who will be able to create firm and powerful weapons from their blood, use their blood to heal themselves, and take full control of the victim's body. I need to find some specific distinction between blood types that would justify making some more receptive to being controlled by another's influence than others. What attribute would I be able to use for this power?