* The series itself is sometimes referred to as Sea Cats/Kittens/Kitties, a pun on the Japanese word for black-tailed gull: Umi -> sea, neko -> cat.[[labelnote:*]] Has been seen in the upcoming fighting game as a bit of GratuitousFrench: "chat de la mer"[[/labelnote]] Numerous characters also have nicknames, which can be found on [[Characters/UminekoNoNakuKoroNi the character sheet]].
** Also [[{{Troll}} "Trolls Trolling Trolls"]] or even [[FourChan "Trolls Trolling Trolls Trolling Trolls"]] for GambitPileup, much of which consists of beings screwing with each other ForTheEvulz.
* Jessica is known to some as Moon-chan, due to her being The Moon in the Tarot deck.
* After her awesome moment in [=EP2=], Rosa is known as Musou Rosa ("musou" meaning "invincible").
** She's also been given the title of [[AbusiveParents BEST MOM EVER]] after Beatrice calls her that in the Tea Party of Episode 2.
* Magical Gohda Chef, which derived from misinterpretation of the engrish ''Happy Maria!' song.
* Beatrice is also known as Beatroll, due to one of her expressions looking suspiciously like 4chan's [[MemeticMutation Trollface]], and because she trolls Battler. A lot. And since Episode 3, {{Moe}}trice.
* [[spoiler:Troll]]kastel. Or, Bernkas[[spoiler:troll]].
* Borrowing from her previous incarnation, you'll still see Lambdadelta called 34. Or Super Paper.
* Eva-Beatrice is Evatrice. [[AscendedMeme Later used in one of the episode previews for the anime]].
* Due to Ronove's callous speech against Beato and good relationship with Battler, he's been frequently called [[BromanticFoil Bronove]].
* Featherine Augustus Aurora is [[HigurashiNoNakuKoroNi Au Au]] by the fanbase.
** And apparently canon, as Bern calls her that.
* [[MemeticBadass WILL MOTHERFUCKING WRIGHT]]
* [[AmbiguousGender Lion]] was called "Zeppeki-san" (Cliff-san) by fans before Episode 7's release, following the train of thought that if Lion were female, her chest must be either bound or, well, flat as a cliffside.
** And of course, in the "main" universe, [[spoiler:Lion was shoved off a cliff]], making this nickname rather [[BlackComedy darkly hilarious]] [[HilariousInHindsight in hindsight]]...
* Natsuhi tends to be given the AffectionateNickname of "Nappi" by Japanese fans − since "ppi" (っぴ) is the result of contracting "tsuhi" (つひ) in Japanese.
* Rokkenjima Prime is a common term used by fans in order to clarify when they are talking about the events on the real Rokkenjima.
* While the location where Battler fights against witches in battles of logic is presumably called [[Literature/TheDivineComedy Purgatorio]], it's more commonly known as [[MetafictionDemandedThisIndex the Meta-World]] by fans.
* [[spoiler: Shkannon]]trice and [[spoiler: Rosa]]trice for the two main conflicting culprit theories.
* George is un-affectionately called "[[GratuitousJapanese JOOJI]]" in the West, to go with his [[TheScrappy Scrappy]] status.