Injustice anywhere is a threat to justice everywhere.
-Martin Luther King Jr.

The King and Queen of Tandraia plus each of their children wear a ring that is at the artifact level, created by Apollo himself. All of these have different color gems embedded within them and the powers of the ring all differ with each ring. Each ring has a major power, a major immunity, and a few more minor powers.

If a wearer of any a ring is killed, there is a retributive power in the ring that gets the one who does the killing punished by Apollo. This is always very painful and the result varies depending on how powerful the person who did the killing is. One other factor is that Apollo is well... Apollo. He favors one of the princesses, Raiena, and well, killing her is a bad thing to do. Darlantan did it once and he was in pain. Lots of it. All Raiena has to do to get Apollo to do something is bat her eyelashes. Dani got one of the rings as well, it used to belong to another daughter, who was killed. Apollo gave the Queen permission to give it to Dani cause the Queen was very worried about Dani needing the help and protection. She's been all but adopted into their family. Apollo also likes Dani quite a bit, which isn't surprising. Take it from someone who knows firsthand from experience with killing Dani, Apollo's not nice to those who kill someone who wears a ring.

Never let pride be your guiding principle.
Let your accomplishments speak for you.
-Morgan Freeman

There must be no tolerance of intolerance.
There must be no freedom to destroy freedom.
-Karl Jaspers