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!!FridgeBrilliance
* The final episode and the OVA reveals that Fujioka Misaki's hair is brown, not black like her sister's...which means the girl at the end of the ED is Fujioka Misaki, not Misaki Mei.
* Why can't Kouichi remember being in Yomiyama or meeting Izumi? Perhaps he was there for his Aunt Reiko's funeral.
* Aunt Reiko's dislike of the mynah bird. It's revealed that she died a year and a half ago and her parents bought the bird as a ReplacementGoldfish. The words the bird keeps repeating "Why, Rei?" and "Cheer up" are what the grandparents said after the funeral. Aunt Reiko hates the bird because it subconsciously reminds her that she's really dead.
* Why is Izumi constantly asking Kouichi if he is sure he has never lived in Yomiyama City? Because he shows signs of being the Extra - the Extra was alive the previous year, died in Class 3-3, and returned without anyone realizing who this is. Kouichi looks familiar but claims he's never lived there. What if he doesn't remember living there because the Calamity has blocked his memory? Granted, the Calamity IS blocking his memory, but for a different reason...
* Why do people in and related to the class all start dying suddenly? The world somehow knows that the "class that invites death" resurrects someone, and it's nature's way of trying to return the world to the way it should be--by killing the person who is supposed to be dead. For some reason, though, the world's worse at figuring out who's the dead one than the people in the class, and simply kills people at random in the hopes of eventually getting it right.
* The UnPerson tactic adopted by the students to protect themselves from the curse is noted to have only a partial success rate to start with. In this particular instance, however, there's actually a specific reason it failed: The Extra this year was never one of the students, so using the UnPerson trick to ignore one student and 'even out' the numbers was doomed to fail that time around.
* Mei and Kouichi seem to get a free pass when it comes to the curse. Yes, both of them are put in danger, and narrowly avoid two separate encounters with falling glass. And yet they are the only ones we know of that actually SURVIVE brushes with the curse (if indeed it was the curse). Moreover, in the last few episodes they are threatened with death directly by a number of students. Those that come the closest to killing them suffer fairly improbable deaths - falling out a window, accidentally hanging oneself from stray cables, and being impaled on glass shards after a lightning strike causes a window to burst open. The curse almost seems to be protecting them both by this point! Perhaps it has a fondness for those the class declares "a person who does not exist"?
** That and The Extra happens to be Reiko Mikami who is doing all she can to protect Mei and Kouichi. Pretty much taking a hit for the former.
* In the ending of the anime, Kouichi asks Mei to check out the nearby amusement park together, noting the conspicuous ferris wheel. Mei replies that she doesn't ride those. Her reason is made clear in the prologue OVA, when her twin sister, Misaki Fujioka, almost died from falling off said ferris wheel. Revisiting would have brought up painful memories of her last visit with Misaki, as well as Misaki's subsequent death to leukemia.
* After the class decide to make Kouichi an UnPerson like Mei, Mr. Kubodera can be heard saying that although the situation is awkward, Ms. Mikami promises to co-operate has best she can. It's awkward because despite the strict division Reiko keeps between her home life and her professional one, she still has to ignore Kouichi at home for the charm to work.
* There is a bit of a verbal pun when it comes to the usage of class 3-3 as the class "closer to death". In Japanese, 4 is a number heavily associated with death. 3, being chronologically before 4, is already close to death by virtue of being one number before it.

!!FridgeHorror
* The rules of the curse are very specific. [[TryEverything How many people had to die for the school to figure out all the little nuances?]]
** A LOT, as they explained in Episode 6.
** They've had 26 years of unfortunate practice, after all.
* We learn that there's a way to stop the curse after it starts up, but making use of it requires being able to identify the "Extra" (impossible in normal circumstances). It also {{RetGone}}s everyone's memories of the "Extra's" existence. Even the person who pulls it off ultimately lacks a RippleEffectProofMemory. So you have a method of stopping the curse that is not only unreliable in and of itself but can not be reliably passed down to future generations, making it unlikely the curse could ever permanently be stopped. Even if the above weren't true and students were able to consistently stop the curse, the memory factor means that overuse could end up causing students to forget the curse altogether, starting the entire cycle back at square one.
* That part in the beginning of the OVA when Misaki Fujioka [[{{the gadfly}} pranks]] a boy into believing that Mei is her doppelganger when the latter approaches them. She even states that a doppelganger is a second you, and that something bad would happen when you see that person. [[{{Foreshadowing}} Sure enough]], Mei appears and Misaki dies by the end of the OVA.