Jeanne and Vanitas

Vanitas is one of the only characters who knows that Jeanne has cravings for blood that occasionally flare up and cause her to behave in a manner similar to a Curse-Bearer, although it is currently unknown exactly what her condition is. After Vanitas finds out, he promises Jeanne that he won't tell anyone, although Vanitas does it under the condition that she never drinks blood from anyone else but him.

Example of:
Secret-Keeper