- Matt received almost no characterization in canon apart from that he loved video games, chain-smoked, and that he was extremely snarky and pretty lazy and messy; despite this, he is almost universally portrayed in fanworks as the Only Sane Man to L, Near and Mello.
- Most fanfic has Matt calling Mello "Mells", while Mello calls him "Matty". You can guess what kind of fanfic this originated in...
- Not to mention Matt's hair. He's never shown in any color pages of the original manga, so a hair color was never defined for him. Fanon decided his hair was a lovely maroon color or cherry red depending on what you like. When the anime came along, he was given a hair color of brown with natural highlights somewhere between navy and dark green, depending on the lighting. Guess which hair color he is still usually drawn with. Also, the fandom decided his eyes were any one of several shades of green. His canon eye color is a deep blue...but the green eyes are as entrenched in the fandom as the red hair.
- Another popular fan theory is that Matt wears long sleeves and gloves to hide evidence of Self-Harm and/or needle-drug use brought on by being separated from Mello. Although he had the sleeves and gloves while both he and Mello were back at Wammy's, as evidenced in Near's flashback in the manga to the Q&A session with L. The simple (albeit boring) explanation for Matt's choice of attire is most likely just that he likes them.
- Also, at the end of Death Note: Relight, we see a Shinigami that is wearing goggles and torn up school clothes, during the scene where Ryuk looks at Light's name in his Death Note. People assume that the Shinigami is Light himself after dying. It was stated in the series that Light was more devious than a Shinigami by Rem, so people think Light got reincarnated because of how he used the Death Note.
- The vast majority of fanfics involving Near say that he's albino despite this never being officially confirmed.
- Many fics also have Near and/or L described as having Asperger's Syndrome, which is also never confirmed.
- Beyond Birthday:
- Beyond Birthday of Death Note: Another Note always calls L "Lawli" in fic as a Terms of Endangerment. Sometimes, they are depicted as twins, or as ex-lovers (and sometimes both); we don't know precisely what their mysterious shared past involved.
- Beyond Birthday being "born with the Shinigami eyes" is often explained that he is either a Shinigami cursed into human form, part-Shinigami, some kind of Death Note owner who just prefers to kill with knives, or the son of female Death Note owner who made the eye deal.
- He is also frequently depicted as a cannibal and/or a rapist, despite there being no indications of him consuming blood and/or flesh from any of his victims in the novel. As for the part about being a rapist, he didn't rape any of them, either; the closest we get to that is his description of himself as an "aggressive top." (Which, yes, could mean that he's a rapist, but it could also mean that he's just into some really kinky stuff or rough sex, or that he's a player.) He never really explains what he meant by that.
- To distinguish Beyond Birthday from L, BB is often depicted with a black shirt (with or without blood splatters), or a white shirt splattered in blood. In actuality, he dressed exactly the same as L, and is way too clean (and too smart) to run around in bloodstained clothes.
- In fanart at least, it's also popular to depict Beyond with red eyes to distinguish him from L. While he does have Shinigami eyes, in the anime Shinigami eyes are shown as Red Eyes, Take Warning only as a stylistic effect, and it's stated in canon that there is no eye color change.
- The author of Zero vs Kira did the math and gives a conservative estimate that if Light did nothing but write names (taking a ten minute break to rest his hand) Kira's kill-rate would be around 1,000 dead per hour.
- Depending on the writer Mello might be German, Russian, Prussian, or Slovenian and he almost always was born with ties to the mafia.
- In many fics, Mello is said to be a practicing Catholic, because he is (particularly in the manga) seen with Catholic paraphernalia in his home and wears a rosary necklace, and also the aforementioned note on his (possible) heritage.(Notably, although Misa owns some Catholic paraphernalia, she is generally thought to just have it because it looks cool.) It certainly also would be a plausible motivation to fight against Kira and his regime, beyond merely besting Near (who he technically gave the role of L's successor to in the series. Also, Mello refers to The Almighty in his introduction to Another Note.
- In almost every fanfic where the topic of Mello's burn scar comes up, the one who treated the burns was Matt, who almost invariably has no medical knowledge, or only some very basic medical knowledge. In the series, we don't know who did, only that the doctors (legitimate and otherwise) that Kira et. al. talked to did not recognize anyone resembling Linda's drawing of Mello. It would have been very difficult (though not necessarily impossible) for a non-medical person like Matt to treat burns that severe note , and not have them get infected or anything.
- The general consensus among the fandom is that Mello left Wammy's on his own, and Matt did not join up with him until after the explosion. However, it's just as possible that they left together. Or that they were separated, but not for the entire 5-year Time Skip. (Maybe only a few weeks or months.) It is also generally believed that they did not have any contact until Mello got burned and called Matt for help, but it's just as possible that they actually did have contact of some kind. (In fact, it would make more sense if they did have contact, since Matt is willing to give Mello the time of day and treat his wounds, but it means less Angst and drama, and we can't have that, now can we?) Also, it isn't known for certain whether they actually were friends (or more) at Wammy's, or if the friendship came later, though the general consensus is that they were very close while there.
- There is a tendency to depict the relationship between Matt and Mello as abusive or destructive in some way. Sometimes, Mello abuses Matt, sometimes Matt abuses Mello, and sometimes the relationship is mutually destructive or abusive. This creates Fridge Logic, when you remember that their few manga interactions show them being nothing if not good to one another, and Word of God states that Mello is always looking out for Matt's well-being (and the reverse is probably true as well). (In fact, it could be argued that they actually have one of the healthiest relationships, if not the healthiest relationship (romantic or otherwise), in all of Death Note!)
- Light's sister Sayu is lesbian. It's never outright confirmed but there are a lot of signs. Less common is her being bisexual due to her mentioning to Matsuda she would have considered dating him if he was younger.
Fanon / Death Note