All Love Is Unrequited: There's a lot of UST, and it either stays that way or shifts to angst. Depending on your definition, there could be one happy couple to come out of this show, but it's a Crack Pairing - Sara and the Throne of Yord.
Double Standard: Abuse, Female on Male: Tiara and Graham's relationship is possibly the most twisted situation in the story, and that's really saying something. Her treatment of him is pretty much a textbook cycle of abuse and reward.
Eye Motifs: If the Throne of Yord has a form, it would be an eye. There are numerous stylized eye images used represent it, from a giant, multi-colored, eye-shaped stained glass window to a primitive stone carving.
Fantastic Caste System: Suggestions of this trope with the way Partners are treated. They are Familiars that border on a Servant Race - sapient beings that aren't given the same amount of social worth as the magic users that summon them. In fact, they're highly expendable.
Gratuitous English: The Japanese voices say "Gaadiaan Warudo (Guardian World)" instead of "Kōken'nin no sekai
Gray and Gray Morality: Tiara doesn't really have any real enemies, more like friends with differing goals at different times.
Homoerotic Subtext: Tiara's muggle friends suggest that the attention she pays to Lena is the result of romantic longing.
I Have the High Ground: The heroines can actually generate their own tall, thin objects to stand on while fighting.
Intertwined Fingers: Tiara and Sara do this at one point. Except it wasn't Sara — it was the Throne of Yord.
In The Style Of: The style of the character design makes viewers think CLAMP was involved in the production of this show, when in fact they weren't. However, the character designer had previously worked on Magic Knight Rayearth.
It Amused Me: The reason why the Throne of Yord does anything. It's eternal, all-powerful, and catatonic most of the time from boredom. It really just liked the idea of having something interesting happen.
Sara/Throne of Yord: I'm just playing. There's no meaning.
Magic Contract Romance: Deconstructed. The fact that beautiful young women are summoning sometimes handsome young men to be their "Partners" which, despite the name, are distinctly subservient to them doesn't always work out too well.
Magic Music: As opposed to Tiara's full-contact method of fighting, Lena uses a flute that manipulates a plant-like substance in battle. It's also used in invoking Leon's transformation.
Rivals Team Up: Tiara and Lena join forces against the Throne of Yord, and even have a heart-to-heart in which they admit that the bad blood between them is fueled by mutual envy.
Scenery Porn: The highly detailed watercolor backgrounds throughout the show.
Screw Yourself: While Tiara, as a child, is trying to tame Graham, her great power manifests as a red-skinned (and naked) version of her powered-up form as an adult. It proceeds to grab her and give her a deep kiss.
Smoking Is Cool: Leon smokes and looks cool while doing so. Lena admonishes him for it, but simply because it's illegal for people his age to smoke in the world where they're staying.
Snow Means Love: It's snowing in Tiara's memories of when she and Kagetsu were together.
Swallowed Whole: Leon and Japolo are making a good effort at defending their partners against the Throne of Yord, then it just shoots out some mouth-tentacles and eats them. And they're gone. Without a trace.