A Blood Bond is a supernatural link of fidelity and dependency of one individual (the thrall) on a vampire (the regent), created and maintained by the repeated consumption of vitae. Virtually anyone can be enthralled through it, making the blood bond one of the most powerful vampiric tools. The strength of this link varies based on several factors, but it is incredibly difficult to break and likely will have many lasting effects on the thrall.
Someone becomes involved in a blood bond by drinking the vitae of the same Cainite on several occasions not excessively spaced in time. After the first sip of blood, the thrall begins to develop strong feelings for the regent, whether love or hate, though they are still free to act as they choose. Those in a one-drink bond may unconsciously seek out the regent, seemingly accidentally running into them on a frequent basis.
After the second sip, the regent becomes a very important person to the thrall, who may go out of their way to seek the regent's attention or please them. It becomes difficult for the thrall to do anything that would harm the regent, and the regent likewise finds it easier to convince the thrall of things. Though the thrall's craving for the regent's blood increases, they still retain their free-will.
After the third sip, the blood bond is complete. The thrall is now subject to the regent completely and loves them as much as they are capable of loving anyone. The regent is the most important person in the thrall's life and takes priority over all else; sufficiently weak-willed individuals will commit any act the regent asks of them. Furthermore, the regent may command the thrall with Dominate via voice alone, not requiring eye contact. It may still be possible for the thrall to act against the regent, but only temporarily and after an extreme effort of will.
The strength of the blood bond is not influenced by the generation of the vampire, but continual drinks do reinforce it. The bond will become weaker over time if the thrall does not drink from the regent's blood and does not see them for a long time. However, due to the very nature of the bond, such avoidance may be extremely difficult for the thrall. The blood bond can be broken by the death of the regent, however, the effect on the thrall is variable: some feel relieved or even joyful; others experience pain and desolation; others yet fear their independence and look for a new bond. A few may even kill themselves.
All childer begin at least one step bound to their sire, and its normal for those that were Ghouls to already be fully bound or for a fledgling vampire to be fully bound to their sire shortly after the Embrace. This was particularly common among the High Clans in the dark ages, when oaths of fealty to a liege were reinforced by some level of the blood bond. The Tremere have their own variation of this custom where all members of the clan are partially bound to their elders and the Tremere Inner Council of Seven.