Fan Nickname / Umineko no Naku Koro ni
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. Numerous characters also have nicknames, which can be found on * the character sheet.
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 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 Trollface, and because she trolls Battler. A lot. And since Episode 3, Moetrice.
Trollkastel. Or, Bernkas troll.
Borrowing from her previous incarnation, you'll still see Lambdadelta called 34. Or Super Paper.
Eva-Beatrice is Evatrice. 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 Bronove.
Featherine Augustus Aurora is Au Au by the fanbase.
And apparently canon, as Bern calls her that.
WILL MOTHERFUCKING WRIGHT
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.
Natsuhi tends to be given the Affectionate Nickname 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 Purgatorio, it's more commonly known as the Meta-World by fans.
Shkannontrice and Rosatrice for the two main conflicting culprit theories.
George is un-affectionately called " JOOJI" in the West, to go with his Scrappy status.