It is a flat black rock that can be used to heal injuries, likely based on the Healing Legacy. When used the pain of healing is twice as intense as that of the actual infliction. In addition, the stone is only of use when the injury was inflicted with the intention to harm or kill the recipient.
It is first used during the Battle of Paradise High School where Six is stabbed with a Mogadorian dagger and badly injured. Unlike most of the objects in the Garde's Inheritances, which can only be used by Loric, the Healing stone can also be used on humans.