Is a concept introduced in Ni No Kuni 2. It is the source of power and connection between a kingmaker and their ruler, that grows stronger over time. However, an object must be used to close the pact and will become the kingdoms treasure, in Evan's case the object was the old stick that Oliver used as a wand in the first game.
It is a powerful bond capable of unleashing a kingmaker's true power. However, if one falls to taint then that will affect one's kingmaker and makes it easier for an outside force like Doloran to steal the other persons kingsbond.