Creator's Pest: Director Mamoru Kanbe was dissatisfied with Nozomi and had to adapt the character out when he produced the anime, despite her being one of the main characters in the manga and singing the titular song.
Executive Meddling: The reason why Nozomi isn't in anime adaptation, because the director hated her.
Fan Nickname: For reference, two names are not official. "The Unknown Man" is the name given by fans since he never gives his name nor anyone else does in the three chapters that he's featured. Also, the term "diclonii" is just the catch-all term given by fans since it is strange to say "dicloniuses" (only "diclonius" has been given officially) and it is the common suffix change, so the name mutated.
The series wasn't released in China due to its graphic violence.
For the longest time, the manga version of Elfen Lied was never released stateside or in any English speaking country (it's speculated to be due to the series being too hardcore for any Western manga company to want anything to do with), forcing fans to read fan translations online (not exactly ideal). Ultimately subverted, as Dark Horse Comics finally stepped up and attained the rights for American release in 2019 (17 years after the manga first came out in Japan).
Kathrin Neusser played Mayu and Kaorin. The fact that both characters look very similar is also an Actor Allusion.
Sleeper Hit: Elfen Lied may be the pinnacle of a slow and continuous success. The anime was so extreme that it could only be aired in Japan via satellite which was done basically just to advertise the DVD set. In 2005, the anime was released in the U.S. and many other western countries to practically no fanfare — initially, but through sheer word of mouth from one anime club to another, and spreading across the internet, the series gained a massive amount of attention in part because of just how hardcore it was that some didn't think it could be possible, and was stated to be one of the bestselling and most notorious anime releases of that year. As time went by, more and more began discovering the series, and over the course of a decade, Elfen Lied may be one of the best-known anime in the west to the point of being seen as a classic and being well-known throughout the internet generation (many famous Youtubers have covered it, even Death Battle). This despite the manga not seeing an English release because no company wanted anything to do with it. The status reached a point where Dark Horse Comics finally stepped up and licensed the series in English for the first time with a 2019 release, 17 years after the debut of the manga.
The "stone stairs", where some of the most emotional scenes take place, lead to the Buddhist Gokurakuji temple in Kamakura. The upper parts of the stairs are part of the temple itself and get closed off at 5 pm every day, so it would not be that easy for the characters to enjoy the view after sunset. In both the manga and anime the gates that block access to the upper part of the stairs are conveniently left out.
Actually, the whole series is set in a real life location, Kamakura. It's very eerie to see the same locations (the dirty beach, the stone stairs, the various shrines and the island with the tower).
Kaede means Maple. Guess where the main character lives...
The entire series makes reference to El Greco's paintings. In almost every episode, characters make a hand sign, which is repeated also in El Greco's paintings.
The handsign mentioned above is a variation on a Hebrew handsign. The whole story is played out like a holocaust as well, with the scientists (nazi-like figures) not only exterminating Diclonii, but also doing cruel tests on them
Lucy is the "mother of all diclonius" according to many characters in the series. She is the only one anyone can find that can breed, and therefore she is the first known ancestor of all of the next generations. She is named after the Australopithecus fossil, Lucy, oldest known human ancestor (At the time): http://en.wikipedia.org/wiki/Lucy_%28Australopithecus%29
Nana is 7 in Japanese, which was her room number in the labs and her age at the start of the series.