Seal (シール Shīru): is a limited Artificial Equipment that's restricted only to certain govermental facilities that utilizes Ki in order to efficiently help or restrain people mentally through the usage of tags. These tags are distinguished though the kanji written upon it, such as Peace, Fear or Focus and once placed upon the designated person, it'll become a seal.
As previously stated in the above, these tags are used to either help or restrain people mentally for a range of different reasons, either it can be for medical, psychic or spiritual aid, even as a way to help an individual that's going through a traumatic experience. This is possible by abusing the fact that each and every human being has Ki inside of them and by connecting this ki with the seal upon ones forehead, this ki can start a process that sends out specific signals to the wielders brain in order to cause some kind of effect. Due to the dangerous possibilities of these seals, they've been banned from ever being used outside of certain govermental facilities, making them a most wanted object within the blackmarket.
When initiating the process from which these tags are to become a seal, the tag(s) can only be created through the usage of regular paper, these are then inscribed with kanji, often in form of short and simple words which describes the tags general effect. Once this is done the writer must then write the rules and or restrictions on the back of the paper that'll explain what the tag will do to the one wielding it and what could happen if the paper ever were to be removed or if it even restricts the wielder themselves from even touching the tag itself. The tag is then finally placed upon the forehead of the intended person before infusing it with a small amount of Ki in order for its description to take effect, should the writer have done this wrong in any way or created a tag which is impossible to perform by the wielder, then the tag will simply vaporize itself after receiving the ki.