Pet

There are people who can get into peoples mind and control their memories. This power is used to eradicate mysteries and cases or worse, to assassinate. The potential of the said power is strong enough that it is able to destroy peoples mind, however, can backfire and eat up their own heart. To counter it, chains are used to lock and protect each others weak and dangerous heart. From ones growing fear and disdain, theyre consequently called as a "Pet."