In Kingdom Hearts, due to the general vagueness of a lot of the inner mechanics of the universe, a couple theories have become embraced by the fandom.
- Master Xehanort's Keyblade, also known as Luxu's Keyblade and the Master of Master's Keyblade, is frequently called "No Name" by fans, despite the fact that it has never actually been called that in-game. The idea stems from the scene where the Master of Masters explains to Luxu that he put his own eye, called the Gazing Eye, into the Keyblade. Luxu thinks the Keyblade itself is called "Gazing Eye," but the Master corrects him that it has no name, leading to Luxu calling it "No Name"note . In fact, the only instance of the Keyblade being explicitly referred to by any name is in a report written by Luxu, in which he still calls it "the Gazing Eye." There actually is a keychain in Birth by Sleep that is explicitly called "No Name," but it's not this one.
- One notable headcanon is the explanation for Kairi's Keyblade. In-game, Riku just gives her a Keyblade out of nowhere during a sequence late in Kingdom Hearts II, which she uses during said sequence and the seems to by her next appearance. Sora gets a second Keyblade in many of his Drive forms. By connecting these two details together, the assumption that gets made is that "copy Keyblades" can be made and either used in the off-hand or given to someone else, with it vanishing when it's no longer necessary.
- This was Jossed in Birth by Sleep, as Kairi's Keyblade (named Destiny's Embrace) was the result of an unintentional rite of succession between Aqua and a young Kairi, whereas Sora and Roxas derive their second Keyblades from Ventus' heart within Sora (contrary to popular belief, Roxas absorbing Xion in Days was not the reason behind Roxas or Sora's dual-wielding). Birth by Sleep also shows that Keyblades can be passed from one wielder to another: Aqua loses her Keyblade, but since she had picked up Master Eraqus's Keyblade prior to this, she is able to summon and use his in its place. The question of how Riku obtained that Keyblade for Kairi, however, is rife for theories, including a popular notion that Riku went to the Realm of Darkness and obtained it from Aqua herself off-screen during either Days or II, or, in light of 3D, the possibility that Naminé, being Kairi's Nobody and having a heart of her own, eventually summoned the Keyblade herself and passed it on to Riku, who then gave it to Kairi. Both are somewhat convoluted, and the former assumption itself was Jossed in 0.2: Aqua managed to meet up with Mickey in the Realm of Darkness near the end of the original game and accompanied him to the other side of the door to Kingdom Hearts that Riku and Mickey sealed from the inside, but is dragged back down into the dark realm when she and the king throw themselves in the way of a swarm of Shadows that was targeting Riku in order to protect him. Riku didn't learn about this until after the events of Dream Drop Distance and is more than a bit upset that they were unable to save Aqua back then given that he clearly remembers their meeting and Aqua's words for him from BBS. It remains to be seen if future entries will shed any more light on this.
- As for their backgrounds before they were Nobodies, it's very common to write Demyx as either a merman from Atlantica or a rockstar. That Xemnas reveals Demyx to have had past history as a Keyblade wielder in III most likely puts a damper on at least the former half of this idea.
- Naminé, like her "other self" Kairi, never had all that much Character Development in the games she appeared in. A lot of fangirls, on the other hand, latch onto her for Fanon, often making her the Yaoi Fangirl to the other Nobodies, or to Sora and Riku.
- While Kingdom Hearts II firmly stated that Nobodies do not have hearts, and therefore do not have feelings, this wasn't exactly shown through their actions, leading many fans to believe that somehow they did have feelings and therefore Sora is a monster to oppose them. While 3D revealed that they were right about the first thing (Nobodies, and for that matter anything capable of thinking of itself as a person, can earn a heart through living life and connecting to others), Sora's actions against the Organization were largely in self-defense against an unambiguously threatening enemy — and even then, he was horrified to learn that Xemnas and Xigbar were deliberately keeping this information secret from them, since they might well not have opposed him if they had known they didn't need to.
- There's a general idea within the fandom that Nobodies have no heartbeat and don't need to eat or sleep. This is despite the fact that Roxas is seen waking up at the start of several of his last days of summer vacation in II and the Organization members are shown to have their own bedrooms in Days. Xigbar even makes a quip to Zexion about resting up for a big mission in a II Final Mix-exclusive cutscene. Jury's out on if characters who lack a heart also have their actual blood-pumping organ affected, but as they're otherwise human, it's not impossible.
- Possibly given a subtle joss in The Caribbean level in III: Davy Jones' heart, just like in the source material, is a literal flesh-and-blood heart as opposed to the metaphysical heart, invoking Wrong Context Magic when the Organization mistakes the former for the latter, meaning that both technically exist in the Kingdom Hearts universe. Assuming that their Empty Shell status isn't an added factor, Nobodies very likely do have a physical heartbeat and a need to eat or sleep.
- Kingdom Hearts II heavily implied that Tifa is the embodiment of Cloud's light (in contrast with the KH Sephiroth being implied as Cloud's Enemy Without) and thus isn't an actual person. It's ambiguous enough, however, for fans to interpret her as a normal character. Almost all fan works portray her as being Cloud and Aerith's friend like in the source games.
- The necklace theory
is a popular fan theory revolving around the meteor shower promise from Chain of Memories. It postulates that, instead of Sora/"Riku" promising to protect Naminé and being given her star charm in return on the night of the meteor shower, Riku swore to protect Sora and gave him his iconic crown necklace. There's solid evidence that Sora's necklace might really have been a gift from Riku after all, as the KHI Ultimania notes that, during development, Sora was originally meant to be given the keychain for Oblivion by Riku, in the same vein as Kairi giving him her Wayfinder for Oathkeeper. It goes on to state that this is why Oblivion's keychain is a black version of Sora's necklace — the implication here being that, somehow, Riku is connected to the piece of jewelry.
