The series is a Whole-Plot Reference to Gosick, which features a savvy Japanese main character finding himself teaming with a petite, long-haired foreign detective girl with some supernatural secrets and who is trying to clean the name of her mother.
Riko's character is also a reference to Kuiaran II from Gosick. Just like Kuiaran, Riko is a blond-haired, female thief from an infamous lineage who poses as a classmate to the main male character in order to manipulate him. She is also a Composite Character with the authentic classmate Kuiaran was impersonating, Avril Bradley, a slightly ditzy, hyper girl who becomes part of the main character's circle.
In the On the Next preview for Episode 11, Aria forgets Kinji's name. She guesses he could be Yuuji or Saito, names of male leads from Rie Kugimiya's previous shows from the Shana wave. Kinji then claims to be Ryuuji, who shares the same Japanese VA as Kinji, and she believes him for a moment.
Being a quiet, mostly Emotionless Girl with short, cold colored hair and uncanny abilities, Reki Yada is an obvious Rei Ayanami Expy, down to her very name (Rei -> Reki) and pseudonym surname (Ayanami -> Yada).
The name of Riko Mine Lupin IV is basically a lawyer-friendly appropriation of Lupin III, as her surnames imply she is the daughter of Lupin III and Fujiko Mine of said work. Indeed, she is said to have been taught seduction by her mother, on account of Fujiko being a famous vamp.
Jeanne d'Arc the 30th the could be easily mistaken for a younger, French version of Saber Lily, with longer silver hair, shorter skirt, and a near-identical sword — with the same seiyuu to boot, to near-Casting Gag levels.
Famous light novel series A Certain Magical Index inspired several references in the series.
Aria's surname probably comes from Index character Kaori Kanzaki.
Jeanne also resembles Jeans Slasher from Magical Index, from the name to the weapon and attire.
Riko's hairdo, ribbons, cat smile and seductive personality are also a clear reference to Kuroko Shirai from manga spinoff A Certain Scientific Railgun.
Elle's name and alias ("L.") are references to another great detective, L from Death Note.
The final shot of the anime's opening credits, in which Aria shoots out a rose, is reminiscent of Saeba Ryo doing the same in the second opening of City Hunter.
Film
As in Speed, a bus has a bomb that explodes if it slows down.
When Reki swears to stay by Kinji's side per The Wind's orders, he raises a leg, in reference to a scene from Terminator 2: Judgment Day where John orders the bot to raise his left leg.
