Precepts (プリセプツ Puriseputsu?) is a term used in Tales of the Tempest to refer to magic. A special type of Precepts known as Life Magic (生命の法 Inochinohou?, "Law of Life") is applied through a catalyst known as a Pensient (ペイシェント Peishento?, "Patient"), a powerful gem that requires large amounts of lives to be sacrificed in order to work.
King Areulla VIII, a Spot from another planet, accidentally hurled himself through space using strange, experimental magic years prior to the events of the story. Seeking to return home, he began to work on a type of Precepts known as Life Magic that could get him back. However, this magic required for thousands of lives to be sacrificed to a mysterious stone known as the Pensient, so King Areulla set about thinking of a way to gather the required amount. Under the alias of a human traveler by the name of "Walls Garner", he deceived the leader of the Leymon people, Couber, into sacrificing Leymon lives to produce Pensients capable of generating enough energy to open a portal, hinted to be the Triverse Gate, to his home world.
The Precepts ritual having failed, King Areulla spends years contriving a new plan, all the while having usurped power as leader of the kingdom of Areulla through unexplained means. He uses the power of Pensients to remain young and lives in an isolated castle atop Mount Ayre to keep this fact hidden while he works on opening the portal that will return him home. One day, a Black Knight discovers this secret and makes his way to the village of Feln, where he is attacked by Spots before giving a Pensient to Caius Qualls, instructing him to take it to the Captain of the Black Knights, Albert Mueller, hoping to reveal the truth to him. The knight then dies, and the following events spur Caius's journey.
Caius himself possesses a Pensient given to him by his late mother, Melissa Bridges, who was petrified during the heretic hunting of the Leymon. Caius was thereafter raised by Ramrus Qualls under the belief that Ramrus was his true father. King Areulla uses the Pope, Vincent Bridges, in the same manner as he did Couber years ago, as Vincent hopes to resurrect Melissa, who is revealed to be his wife. King Areulla commands the Pope, who commands the priests of the Church into hunting the Leymon in order to acquire more Pensients, as the technology is partly theirs. The Church's priest-soldiers likewise are shown to possess and use Pensients to petrify Leymon who resist arrest.
Pensients, and to an extent, Life Magic, do hold the ability to extend lifespans dramatically, but they are never proven to restore life. King Areulla merely uses this ploy to deceive his victims so that he may garner enough energy to return to his home world, using the power of the Pensients to avoid growing old in Areulla. His intentions are purely motivated by evil, however, as he pays no heed to the lives lost and seeks to become the king of "both worlds" in the end. Ultimately, Life Magic is a forbidden branch of Precepts that yields far more negative aspects than it does positive.