- Author Existence Failure: Yamaguchi died on April 4, 2013, after losing a two-year battle with cancer. Thankfully, Denko Bunki (the publisher of the novels) announced two years later, on June 25th of 2015, that the series would be completed posthumously, as Yamaguchi dictated the finale to his editors from his sickbed. The last two volumes concern the true nature of the Void, Brimir, and the origin of the conflict between humans and elves.
- Fan Nickname:
- Fandom-Specific Plot/Obvious Crossover Method: The sheer amount of Crossover fanfics where Louise summons someone else instead of Saito in mind-boggling. It's so popular that there are fics for it where Louise summons something that really shouldn't be summoned.
- Additionally, Siesta's ancestors are usually changed to be from wherever Louise's familiar is from.
- Although it's partially a natural response to the sheer Fanfic Fuel of the Familiar Summoning Ritual, the vast majority of such fics also fall under Fix Fic territory: the fanfics invariably are based on the ground of discontent with Saito's character arc, or as a negative response to the Double Standard: Abuse, Female on Male and Happiness in Slavery of the canon. This is especially common with "superpowerful" familiars.
- No Dub for You: Seasons 2-4 are being released sub only.
- Official Fan-Submitted Content: Just like in the Spanish-language dub of The Sacred Blacksmith, Louise and Saito's voice actors in both the Mexican and European Spanish dubs were selected by the fans. In both versions, rather than using well known voice actors, both dubs used newcomers for both characters.
- Outlived Its Creator: Noboru Yamaguchi died of cancer in 2013, with 20th light novel volume of the series released 2 years prior but with some material to release the following volume ready, the series was nearing its climax and was a constant hit in sales; Noboru had rough notes and manuscripts of how the series would end, with this the publisher Media Factory decided to pick someone capable of finishing writing the series in his place, 2 more books to end the series at the 22th volume were scheduled, in February 2016 the 21th volume finally reached the stores, the new author was being kept in secrecy, Noboru Yamaguchi being credited as the sole writer as tribute. The new author was since been revealed as Yū Shimizu of Bladedance of Elementalers.
- Relationship Voice Actor - Satoshi Hino and Rie Kugimiya. Saito and Louise. This speaks for itself.
- In the English dub, at least, Tabitha and Kirche, the quiet young mage with serious parental problems and her busty, energetic redhead best friend, are also Fate Testarossa and Arf... a quiet young mage with serious parental problems and her busty, energetic, redhead familiar.
- Louise (Cristina Valenzuela) and Kirche (Lauren Landa) can be heard in as Noel and Litchi, Homura and Kyoko, and Rei/Sailor Mars and Michiru/Sailor Neptune.
- The same happens in the Mexican Spanish dub with both Saito and Louise's voice actors, as they return again in the Mexican dub of Naruto Shippuden: Ultimate Ninja Storm 4 as another Battle Couple: Boruto and Sarada respectively, and also in the dub of Trolls as Guy Diamond and Bridget respectively as well.
- Series Hiatus: The release gap between volumes 20 and 21 is about five years. Justified though, given that Yamaguchi got sick with cancer and died.
- Star-Making Role: In the Mexican Spanish dub, for Louise and Saito's voice actors (Annie Rojas and Jose Angel Torres respectively)
- The Wiki Rule: The Zero no Tsukaima Wiki and The Familiar of Zero Wiki.
Trivia / The Familiar of Zero