The theme playing at the very beginning of the pilot is a chanted variation of the taize prayer Kyrie Eleison, which is Greek for "Lord have mercy."
The theme that plays at various key moments - the "I am Justice" duet, the capture of the Yotsuba Kira, the revelation of Light's final gambit against Near, and the timeskip montage (where it plays in full) - is a Dies Irae. Oddly, it does not include the fifth verse of said apocalyptic choral number ("The written book will be brought/In which all is contained/Whereby the world will be judged"), but that is covered in "Teleology of Death", which plays when less overblown Ominous Latin Chanting is called for.
Mello and Near's character designs were accidentally switched during character creation explaining why they have Ironic Codenames—they were originally going to be Meaningful Names—Mello was intended to be the "mellow" one and Near was intended to be the Axe-Crazy one who was drawing "near."
Aruno Tahara, who voices the George W. Bush-looking US president in the Japanese version, previously dubbed George W. Bush in Fahrenheit 9/11.
In the Latin American Spanish dub, Misa Amane's voice actress (Rebeca Gómez) voiced Mandy, a girl who's friends with the western version of a Shinigami.
Ascended Fanon: Originally, L's knowledge of capoeira was simply put in because the writer was thinking of ways that one could fight while handcuffed to their opponent. But then some fans pointed out that it looked like capoeira, and eventually in Another Note, it became canonical that L has some knowledge of that particular martial art. Though the canonical status of Another Note is hotly debated. It's mentioned in the manga reference How To Read, but isn't by the original mangaka, and several things in it appear to either be outrageously untrue (such as the third World War having happened in a world mostly similar to our own) or otherwise clearly inconsistent with the anime and manga canons.
Banned in China: The series was banned in China for allegedly inciting anarchy and insubordination, after some kids and teens were caught using ripoff notebooks to make hit lists. That being said, it did receive a Cantonese dub and was aired in Hong Kong.
Episode 2 of the anime has a minor, but noticeable animation error during the shot where Light holds up the Death Note while declaring that L can't catch him without finding it first. The last frame loops a couple of times, making it look like Light randomly decided to put down the Death Note and then hold it up again for no reason.
Directed by Cast Member: In the Latin American Spanish dub, Rolando de Castro is the ADR Director as well as the voice of Ryuk.
Fandom Nod: The interstitial factoids in the manga.
Flip-Flop of God: In the How To Read volume of Death Note, Tsugumi Ohba (the writer) stated the L was the most intelligent character in the Death Note series because the plot required it. However, in the very same book, his intelligence was rated 8/10, compared to Light and Near's 9/10.
No Export for You: There are three DS games produced by Konami, four of the DVD collector's figures (Soichiro, Takada, Mikami and the King of Shinigami) and the anime guidebook, all not released outside of Japan.
One-Take Wonder: One of the most beloved moments across the 12 different versions of the anime, the Italian take on Light's Evil Laugh in the final episode, was done on the first take.
The TV drama uses a completely new cast, recasting even Ryuk who is voiced by Jun Fukushima instead of his original voice actor, Shido Nakamura. This, along with the musical, is the only time that Nakamura has not reprised his role.
In the series' English dub, the only inconsistency was the FBI Director, Steve Mason. For his phone call to L, Michael Dobson provided his voice, but after the Time Skip it was changed to John Novak.
Promoted Fanboy: Doubly so for Hugo Núñez, who had read the Death Note manga, novels and movies and become a fan of them long before he even knew the anime was going to get dubbed in Latin America - and at the dubbing studio he was working for, no less. He eventually got cast as L, who happened to be his favourite character in the series (he even has his letter tattooed in his left arm).
Ohba decided that the third Kira would be Higuchi by essentially undergoing a process of elimination - after establishing Mido and Takahashi as Red Herrings and deciding that Shimura didn't have the right personality, he picked Higuchi to be Kira based on Obata's remaining designs.
One of the major turning points in the early story (and one of Light's first mistakes) is when he pauses to gloat at Raye Penber as he dies. Penber's death is caught on security camera and L watches it. The way Ohba drafted it in his thumbnails, Light just says "Good-bye, Raye Penber," and moves on his way, but when Obata drew it, he staged it in such a way that L could clearly see Raye Penber looking at someone in recognition off-camera. While Ohba did not script the scene that way, he utilized it by having L realize that Raye Penber's killer must have been someone he knew, and thus he zeroed in on the people Penber was investigating... like Light.
Technology Marches On: At one point in the story, Light has to buy a small portable television in order to covertly listen to the news while his room is bugged. Had the story been set a decade later and he owned a modern smartphone, this might not have been as necessary.
The author originally intended to use Mogi for an awesome and epic plot development, but could never figure out what that would be (beyond it being awesome and epic).
According to How To Read 13, the entire task force were going to die in heroic ways. In the actual story Matsuda, Aizawa, Mogi and Ide all survive.
Ryuk was originally going to look like this◊ but the creators were worried that if he looked cooler or more attractive than Light then the fans wouldn't pay attention to Light.
According to How To Read 13 for that scene where Light and L are "getting to know each other better" the creators were originally thinking of having Light and L do a fencing duel before ultimately settling for tennis instead.
Also according to the How to Read 13, Mello was supposed to be the one who defeated Light, not Near. Ohba ended up killing him off though due to him learning too much about the Death Note, meaning if he were kept alive much of the tension in the series would have gone kablooie. Both Ohba and Obata admitted to liking Mello better than Near, with Ohba saying that being told Obata also preferred Mello probably would have been enough to change the ending back to Mello winning.
Naomi Misora was also originally going to be more of a major character, but Ohba had to kill her off quickly as it was felt she'd complicate the story by being too smart and figuring things out fast.
How To Read also mentions that in the planning stages it was briefly considered that Mello and Near would be L's twin sons but that idea was scrapped, likely as it would mean someone like L actually managed to have sex with a girl and the author just couldn't see that ever happeningnote as well as with L being 25 at the time of his death and Mello and Near being young teenagers when they're introduced, that would have brought up some Unfortunate Implications about the age of their "father", so Mello and Near became Tyke-Bomb orphans instead. Mello was also going to have white hair, as seen in an early color poster featuring the younger versions of him and Near (on the main page), but had his hair changed to blond by the time Obata started doing color images with his adult self.
The high-ranking Daril Ghiroza was originally going to play the role that Sidoh ultimately did, but this was scrapped because of her complex design, and her having a high ranking wouldn't look good against her being "pushed around" by humans.
Tsugumi Ohba's and Takeshi Obata's next series, Bakuman。, had a thinly veiled Self-Deprecation in which a series that was a stand-in for Death Note was being pressured by the editor to continue dragging the story out past the main rivalry. This leaves the impression that Ohba and Obata originally did not plan for the series to continue past the "Light vs L" plot.
Writing by the Seat of Your Pants: Ohba admitted to doing this in an interview; Obata, who was present at the time, was shocked and thought Ohba was joking at first.
