Everyone, humans and shinigami but especially the main characters, are subject to this.
* Light Yagami, an [[AxCrazy unrepentant serial murderer]] with a major [[AGodAmI complex]], [[WellIntentionedExtremist idealistic if somewhat deluded young man who means well]], even if, ultimately, the ends don't justify the means, [[DarkMessiah the savior of all mankind]], or a WoobieDestroyerOfWorlds? That's just the tip of the iceberg.
* Take L: is he a borderline-sociopathic KnightTemplar [[NotSoDifferent scarcely any better than Light]], an AntiHero whose methods are questionable but who is not really ''evil'' ''per se'', or just an endearingly [[NoSocialSkills socially inept]] genius with a difficult past who has had lifelong problems fitting in? WordOfGod calls him 'slightly evil', which seems to fit in best with the second interpretation, but even that's probably up for debate. Then you have the much-debated question of whether L and/or Near have some form of autism. You decide.
* Near and Mello both get it, also. Does Near dislike L? Does he hate Mello, does he secretly feel friendship for him, is there massive amounts of HoYay involved? Is Mello Catholic, or is there [[CreepyCoolCrosses some other reason]] he'd wear a rosary? Is Mello an AntiHero or an anti-villain? Is Mello a super-temperamental guy, or is it just that Near pushes his BerserkButton? A fanfic claimed that Mello was faking his insanity to throw Near off. And then there's Matt, who didn't even have that much of a personality, so that subject is pretty open. About the only things consistent are the fact that he's a techie who likes games and he's pretty lazy. Then you get into Misa, Ryuuk, Mikami, even Takada.... Death Note has massive amounts of this sort of thing.
** In the manga's last chapter, Near can be seen playing with his models, but also eating a bar of chocolate, which could count as him respecting Mello's memory. Similarly, the fact that he begins to call himself "L", but with a different font, implying that he did not, or rather can not replace him.
* There's also the endless debate over whether or not [[spoiler: Matsuda's speculation that Near used the Death Note to restrict Mikami's actions is true, though this theory works less for the anime than it does the manga; in the anime, Mikami commits suicide during the final confrontation, while in the manga, he inexplicably dies some time afterwards, which Matsuda considers possible proof that he was written into the Death Note. WordOfGod also mentions that Near "cheats."]]
* There's also Misa Amane. Is she just a naive young woman whose traumatic past lead her to idolize the one person in her life whom she percieved as being on the side of justice and righteousness (regardless of whether he actually was), an emotionally disturbed [[PsychopathicManchild woman-child]] who is unable to comprehend the notion that human life has any value other than fulfilling her own hedonistic desires, or a nihilistic sociopath who casually declares the act of tricking someone into loving you so much that they would lay down their life for you "a beautiful way to kill?" The series itself can support any interpretation.
* One common Alternative Character Interpreation for any Death Note user is whether or not it's the power over life and death bringing out their darker side, or if just ''using'' a Death Note will drive a human absolutely batshit insane. There is a ''marked'' difference in Misa, Light, and Mikami's mental stability and personality depending on whether or not they have a Death Note at the moment. As such, Misa can be argued to fit the first interpretation when she's in her right mind, and the second when she's in her "2nd Kira" persona.
* The shinigami's are questionable in some cases, specifically Rem: is Rem a good shinigami looking out for a human she/he fell in love with, or is she/he still a monster that survives by killing? Also, are any shinigami's evil, in that they were made to kill people therefore are only fullfilling their nature?
* Taro Kagami from the pilot chapter. [[spoiler:Throughout the story, he comes across as a genuinely good kid who simply got thrown into horrifying circumstances way beyond his control. The pilot's ending, however, is very open-ended. We know Taro kept the Death Note. It's unclear whether he simply kept it or if he did a FaceHeelTurn and started using it again. Unlike Light, whom WordOfGod specifically identifies as "evil," Taro is someone whose moral alignment is genuinely open to interpretation.]]
* Also, anyone in the main story. Is Light a psychopathic depraved lunatic with delusions of godhood who kills people indiscriminately for a reason which has been inherently deconstructed? Or is he just a nice guy trying to do the right thing and is in fact the second coming of Christ? Similarly, with L: is he a brilliant chessmaster with a desire to stop a mass-murderer, a talent for reading human nature like an open book, and a genius that surpasses Light (considering he didn't have a Shinigami and all...)? Or is he just a paranoid neurotic who manipulates and schemes to destroy the heroic Light and ruin the utopia that he is trying to create, and is in fact the anti-christ in human form? [[InternetBacklash Apparently either interpretation will get you ripped apart by ''someone'' on the right forum...]]
* As for Light himself, [[spoiler:it is implied that the power of the Death Note corrupts the user, and when Light returns the Death Note to Ryuk, he loses all memories of his killing and actually asks himself whether he'd be capable of killing. So is the Death Note actually responsible for Light's murders as Kira, or was he just a rotten individual all along and just drunk with power?]]
* Some people also noticed after [[spoiler: Ryuk took away his knowledge of the Death Note, but he regained it later,]] Light acted like he had [[GollumMadeMeDoIt multiple personality disorder]]. You can supposedly see it in his eyes: when his eyes are slanted he's Kira and when they're round again he's switched back to Light. Of course, near the end of the series, [[spoiler: Kira takes over, and his eyes don't turn round again until the very last episode.]] Re-watch the scene in the anime when [[spoiler: L dies.]] Light's eyes switch from pointed to wide while he's falling out of the chair, and [[spoiler: he suddenly goes insane, grabs L and starts screaming. After Rem dies however, his eyes are pointed again and he's perfectly calm and collected again.]] Also [[DoubleConsciousness he does tend to dissociate from his actions as Kira]], even when he doesn't ''need'' to, for instance, in the manga when he explains to Ryuk: "If I blow it, ''[[ThirdPersonPerson Kira]]'' may have to kill his own family."
* There's also the question: Did Light really have a "perfect life" or did he have [[FreudianExcuse a crappy childhood?]] [[http://witegots.deviantart.com/art/277-DN-Genius-Yearbooks-75939490]]
* Another interpretation is Souichiro is MarriedToTheJob and Light is WellDoneSonGuy and [[FreudianExcuse part of Light's hatred of criminals]] stems from the fact that they took his father away from him. When Kira gains the attention of the Japanese police he really does run with it because he finally got daddy [[AttentionWhore to notice him.]]
* Not to mention when [[spoiler: his father died.]] Did Light cry because [[spoiler: his father]] [[YouHaveFailedMe failed to do what he wanted him to do]], or was Light breaking out of his possible brainwashed state and was [[MyGodWhatHaveIDone horrified to see what he has done]], what he'd become, and [[DespairEventHorizon realized whom he just lost]].
* Also, in the anime, while running away, he saw a younger and more innocent version of himself. So did Light die trying to escape arrest, or was he [[DyingAsYourself brainwashed and snapped out of it]] while running away and thus, tried to find a place to hide to die alone.
* Another interpretation-Light was fully expecting to be punished for using the notebook but then Ryuk comes along and tells him there isn't any punishment and he's not going to kill him as long as he's entertaining. Light adapts accordingly. So when he gives his MotiveRant in the first episode about killing criminals and being God of the New World it wasn't his original goal but Light being a MasterActor was telling Ryuk [[ScheherezadeGambit what he thought he wanted to hear in order to make himself seem more interesting and have the demonic creature spare his life]]... and then he got LostInCharacter.
* Another interpretation is that Light actually does care about his family. While some fans question whether he gave a damn about his father dying, some would argue he ''does'' care about them, and is actually a {{Yandere}} that wants to make the world a better place for his family like a [[CodeGeass certain other character]].
* Another Mello one. Is he an overly-emotional good guy with an inferiority complex who's tired of being AlwaysSecondBest, or is he an evil selfish AxeCrazy ManipulativeBastard? Or both? Yeah...both.
* Near.
** He openly states that good and evil are purely subjective concepts, and whilst this doesn't necessarily disqualify someone from being Good or Evil, he never shows any inclination towards either, pursuing Kira both because it's what L would do and in order to avenge L. in the manga, [[spoiler: it's heavily hinted (or rather speculated by Matsuda) that he kills Mikami with the Death Note in order to get final revenge for L.]] However, this detail is omitted from the anime, and in general the focus of his character is more on becoming L's successor than avenging him.
** On that last point: while WordOfGod states that [[spoiler: readers are meant to draw their conclusions about whether or not he used the Death Note on Mikami]], [[spoiler: Obata describes him as "dishonest" and "the more evil" of him and Mello.]]
** This is [[FlipFlopOfGod complicated further]] by the fact that Obha has spoken more favourably of him, describing him as "blessed from above" with L's brainpower, so it really ''is'' open for interpretation.
* Could it be that Near actually dislikes L since he does [[spoiler: wear his mask in the warehouse scene, and coldly says, in response to his death, that those who can't solve the case are simply losers]], or could he actually respect him judging by the fact that he admitted he [[spoiler: couldn't beat Light alone, and tells Light, while he's acting as the second L, that while L made substantial progress on the case, Light has done almost nothing]].
* Misa. Could it be that she actually is just an AxeCrazy {{Yandere}} or it could be argued she might have actually had some sort of trauma considering how dependent she is on that ''one'' person (Light).
** It's explicitly spelled out in the series. Misa became obsessed with Kira, and therefore Light, because he killed the person she watched kill her parents.
* Souichiro Yagami. WordOfGod states that he is the only character that truly fights for justice. He is quite definitely determined to catch Kira for the sake of justice, but also objects to L's more unorthodox (and less savoury and lawful) methods. However one may question just how "just" threatening an unarmed civilian at gunpoint really is. Not to mention [[spoiler: making the trade for Shinigami Eyes and attempting to write Mello's name into the Death Note, only failing to write said name in full because Mello asks him if he's ever killed a person, leading to a moment of hesitance which proves his undoing.]]
* Raye Penber's StayInTheKitchen line. Is he a misogynist, or does he just want his future wife to live a normal life as a housewife so she will no longer be in the risky trade as a law enforcement officer? (For what it's worth, in the films the line is out of genuine concern for her well-being.)
* From the live action movies there's Light's girlfriend Shiori Akino. Is she a) [[TheIngenue genuinely clueless]] or b) she knows / suspects Light is Kira and [[SelectiveObliviousness is in denial]] or c) she knows / suspects Light is Kira and is [[CoolDownHug trying to talk him out of it.]]
* I'm surprised Matsuda hasn't been mentioned yet. He's definitely a much better agent than he seems. For one, he's able, ''under pressure,'' to XanatosSpeedChess his way out of a dangerous situation with the Yotsuba group, using an alias he was barely familiar with, all within seconds. Then, he's able to act convincingly drunk, do a ''handstand'' on a balcony ''several stories up,'' and ''drop onto a mattress a floor down,'' all without showing fear or breaking character.
** Furthermore, in the finale, he's under emotional distress, but his hand is still steady enough to ''shoot a pen out of Kira's hand.'' CrouchingMoronHiddenBadass, anyone?