A Scion is one of seven individuals that are either on the side of Arceus or the original entity of CHAOS, Diazacul. They each represent one Heavenly Virtue or one Deadly Sin. On the side of Arceus you have Purity, Humility, Temperance, Kindness, Patience, Charity and Diligence. Conversely, on the side of Diazacul, he is represented by Lust, Pride, Gluttony, Wrath, Envy, Greed and Sloth. These Scions are the respective champions of their chosen god and are destined to face their opposite.
In many stories, Scions are normally referred to as ‘the Children of Arceus’ and called saviours of the world. People in ancient civilizations believed them to be messiahs sent by the Maker to save mankind from evil and temptation. Their true purpose, however, is to instil change in the world.
The original Scions were beings blessed by the light of Arceus. Those lights, in time, were passed along within the bloodline of humanity.
As only 7 Scions can exist at a time, no other Scion may be born until one has passed away. In most cases, Scions will not have a Scion for a child (unless under the most extreme of circumstances) and thus having more than one Scion born in the same family is rare, especially if both are still alive. If, somehow, a Scion is born in the same family as another, the Scion gene would have skipped at least one generation to space things out between each divine existence. Although this is rarely the case and the soul of the departed Scion would move on into another family line, as directed by Arceus himself.
If need be, Arceus can stack the chances of Scions being born as Heralds as well, though they are never born as Guardians or Heroes. However, this has only truly been done twice in the case of Arceus, with the Herald of Giratina being the most recent attempt.
For CHAOS, they are not so much born as chosen and nor are they like traditional Scions. They are more often than not, ordinary men and women with extraordinary ambition that attracts Diazacul’s attention. To date, the only true Scions of Chaos were Ceraeion Fieorel and the departed Ghetsis Harmonia, now going under the name of Perses, though the latter was made artificially through means of something akin to alchemy.
Powers vary from Scion to Scion, depending on whether or not they are a Herald, already possess abilities like Aura manipulation, psionic powers and the like inherited from parents or a bloodline trait. These powers are specific to Scions of Arceus only.
The Scion’s main power is to purify Chaos. Some may siphon it and purify it within themselves, like a tree takes in carbon dioxide and lets out oxygen. Or they could do it with a touch, basically burning it out of someone’s system with holy light.
The Scion’s second ability is to take on abilities of a Pokemon that is closest to them at birth and eventually those they become close to as time goes on. The stronger the bond, the more able a Scion is to copy or use a Pokemon’s abilities. Rosa, for example, became a very powerful empath due to her proximity to her father’s Ralts at birth, however hers has to do with the sound of a person’s voice rather than feeling those emotions like a psychic empath would.
Thirdly, they had a specific trait that makes them stand out. Their particular virtue, which would inspire change within the people they would meet.