Binding is a method of partially or completely fusing the souls of Abyssal and Exigal creatures. It is a complex ritual that can only be performed by a class 3 entity or higher, as other beings do not have the ability to connect with the opposite realm.
The most effective and common method requires a being to bring a portion of blood into Abyss with him, as it will allow the shard to see that person's presence in the Abyss. The amount of blood will also determine the strength of the binding. The being then needs to bring the creature they wish to bind to the same relative location as the host, and the entity being bound must ingest or be saturated in the Host's blood. Both the abyssal and the human must be branded using vis. Neither the human nor the abyssal necessarily need to be alive to be bound. Other methods involve simply branding the participants with pure vis for a weaker binding, or a complete fusion of the soul in rare, dangerous, and often illegal cases.
The amount of blood, the strength of the participants, and other criteria factor into the result of the binding.