A-tan, fairly sure that they made the implication, if not outright declaration that white whistles were made from people. It was when the MC got her white whistle that it happened... And, yes, each white whistle has its own property (likely due to who it was made from).
Now, the following is what I am less sure of: the person that makes a white whistle has to either have a strong desire to explore, or (more likely) protect the one who recieves the whistle.