Planetary Spirit Magic

Planetary Spirit Magic (惑星系精霊魔法, Wakuseikei Seirei Mahō) is an ancient, powerful, and revered form of Spirit Summoning Magic that's existed since the early stages of humankind; it was one of the few methods that man used to communicate with the divine and supernatural, drawing upon their power to meet their ends. Typically, it's considered to be a Holder Magic due to its method of employment (via a unique set of ancient keys), and counted as one of the few forms of Lost Magic. It's also closely related to Celestial Spirit Magic, as the two have various aspects in common, though it's unknown which one existed longer.

As the name would imply, the user is able to conjure the spirits of the planetary bodies — whose strength is rumored to be immeasurable. It's said that this magic is hard to control, as the spirits themselves are very selective of their owners, refusing to serve those who don't meet their qualifications. It's said that this magic appears once every few centuries and that it's considered to be one of, if not the strongest form of spirit summoning there is, barring the vast scope of Spirit Slayer Magic.

Overview
"Contracter, do you know why I chose you to wield my key, and thus my vast powers? It's because you have the qualities that I see most in myself. That's right, you basically remind me of myself, thus it's easier to understand and work with you. Be grateful for having such traits. It's the only reason why I'm working with you."

- A Planetary Spirit displaying its nature when stating its reason for its partnership.



Trivia

 * The genders, abilities, relationships, and personalities of each of these spirits align with their mythological counterparts.
 * The author states that the reason for their power level is because he confirmed that they're one of the few forces in the Heroic Chronicles universe that can match a God and their role in certain arcs will be rather critical in relation to such beings.
 * Due to the amount of magic required to summon a spirit, he states that there will only be one spirit contracted per user to prevent them from being overpowered. Not to mention that they're like trump cards, holding more sway than all other forms of spirit summoning seen to-date. He also confirms that they're the only race of spirits immune to the effects of Spirit Slayer Magic. Instead, they are heavily affected by God Slayer Magic because of their representation and their status as divinities.
 * Their repsective images are derived from the Yu-Gi-Oh! franchise.