* AngelDevilShipping / MindGameShip / {{Foe Yay}}: [[spoiler:Kuroha]]/Mary is rather popular with some fans despite their interactions with each other in [[spoiler:Outer Science]] being decidedly [[EvilGloating less]] [[ForcedToWatch than]] [[EverybodysDeadDave friendly]].
* BaseBreaker: Momo. Her fans like her for being the most [[AngstWhatAngst upbeat]] [[GenkiGirl girl]] among [[WorldOfWoobie the cast full of woobies]] and for doing her best to cheer up [[DeadpanSnarker Hibiya]] after his incident with Hiyori. Her detractors however, find her backstory to be forced and her character to be boring, and they also complain about Momo [[SpotlightStealingSquad tending to wrest away the spotlight]] from the [[GenericGuy more interesting characters]]. Her being one of [[CreatorsPet Jin's favorite characters]] doesn't help. Might count as FridgeBrilliance considering her eye ability.
** [[spoiler: Kuroha]] too in some smaller circles, due to the fact he mostly serves as a plot device and originally wasn't even supposed to be part of the story until he was inserted into an official Music Video. There are also people who get annoyed whenever [[DracoInLeatherPants fans are diehard for him]], finding him overrated.
* BrokenBase: There seems to be a division within the fandom Shaft's renderation of Kagepro. Some people beileve Shaft is doing an amazing job at it while others feel Shaft is being lazy. [[RuleOfCautiousEditingJudgment Any more on either side seems to light very heated discussions.]]
* CrowningMomentOfHeartwarming: ''Moon Viewing Recital'' as a whole. Especially considering it came after many really [[TearJerker depressing songs.]] [[ManicPixieDreamGirl Momo's]] interactions with [[DeadpanSnarker Hibiya]] are all too cute, and it's nice to watch Momo help Hibiya slowly get over his SurvivorGuilt was very nice to watch. [[AwLookTheyReallyDoLoveEachother Shintarou watching out for Momo at the end made it sweeter.]]
** ''Summertime Record'', and the fandom's response to it. [[spoiler: Ayano would be proud.]]
* EnsembleDarkhorse:
** [[MessianicArchetype Ayano]], who was already pretty popular way back when she was first introduced in Toumei Answer (in which she served as {{The Lost Lenore}} to Shintaro). [[spoiler:And when she was confirmed to be [[BigGood Mekakushi Dan's founder]] and Kido, Seto, and Kano's [[CoolBigSis surrogate older sister]]]], her popularity skyrocketed and she's now arguably the most popular female character, pretty impressive given that she's a {{Posthumous Character}} only seen in flashbacks.
** '''Kuroha''' due to being [[spoiler: EvilIsCool and EvilIsSexy. He's also loved for his general PsychoticSmirk and AxCrazy nature making him a DracoInLeatherPants.]] It helps that he has heavy plot relevance and his song Outer Science is a WHAMEpisode that's catchy.
** The [[FanNickname Mekakushi]] [[PowerTrio trio]]: [[{{Kuudere}} Kido]], [[NiceGuy Seto]], and [[TheTrickster Kano]], all have a large number of fans.
** Mary also has her own dedicated following, since her general innocence, shyness, and being TheKlutz make her very endearing to fans.
** Hibiya has his fans largely due to being an adorable [[LittleMissSnarker snarker]] and for having the most iconic song in Kagerou Days.
* FanPreferredCouple: [[BroodingBoyGentleGirl Shintaro/Ayano]], [[MasculineGirlFeminineBoy Haruka/Takane]], and [[RescueRomance Seto/Mary]] all receive enough {{Ship Tease}} to be borderline [[OfficialCouple canon]]. [[BelligerentSexualTension Kano/Kido]] is a bit more [[WillTheyOrWontThey in the gray area]], but the pairing is nevertheless incredibly popular with fans. [[ToyShip Hibiya/Hiyori]] could also count, or alternatively, [[LikeBrotherAndSister Momo/Hibiya]].
** For the {{Ho Yay}} variant we have [[ChildhoodFriends Seto/Kano]] and [[HeterosexualLifePartners Konoha/Shintaro]] or [[spoiler: [[{{FoeYay}} Kuroha/Shintaro]]]]. For the {{Les Yay}} variant we have [[TomboyAndGirlyGirl Kido/Momo]] and [[RomanticTwoGirlFriendship Momo/Mary]].
** While not as popular as the above pairings, [[SavvyGuyEnergeticGirl Shintaro/Ene and Kano/Momo]] both have their fans. It helps that the former pairing doubles as VitriolicBestBuds while Kano is prone to flirting with Momo.
* HollywoodPudgy: According to Kido and Shintaro, Momo's quite heavy.
* LateArrivalSpoiler: Haruka and Takane being Konoha and Ene's former selves is considered common knowledge among the fandom. It's also hard to talk about Ayano's importance to the plot without eventually mentioning her being Mekakushi Dan's founder and surrogate older sister to Kido, Seto, and Kano.
** Additionally, the fact that Hibiya is listed as a member of the Mekakushi Dan should be a big enough hint as to who survives the TimeLoop between him and Hiyori.
** Early on in the anime's airing, new fans had gotten upset over being spoiled about certain things such as characters having eye abilities- something that is considered the most basic knowledge among the fandom.
* MemeticMutation: "May soda be eternal".
** [[spoiler: Kuroha]] being associated with bees, in reference to his color scheme.
** "Welcome to my womb".
** Konoha's expressions in the announcement of his voice actor.
** "Maternity Spiral"
* {{Moe}}: [[CuteMonsterGirl Mary]], [[GentleGiant Konoha]], [[NiceGuy Haruka]], and [[PerpetualSmiler Seto]]. While [[AdorablyPrecociousChild Hibiya]] is often portrayed as a BrattyHalfPint, Otsukimi Recital just goes to show how adorable the little guy is beneath all that [[DeadpanSnarker snark]].
* MoodWhiplash: In the Mekakucity Records cd, [[NightmareFuel Outer Science]] plays after [[TearJerker Re:Gunjou Rain]]. And after Outer Science? The upbeat Otsukimi Recital, followed by Lost Time Memory.
** The order in which the music videos were released as well. After Konoha's State of the World, a continuation of Heat Haze Days, Kisaragi Attention was released, which is one of the happiest songs in the series. And following Yuukei Yesterday's release was the [[NightmareFuel Nightmare Fuel-induced]] Outer Science. [[CrowningMomentOfHeartWarming Summertime Record]] was completed two days after.
** Chapters 17 and 18 of the manga. In Chapter 17, we're finishing off Takane's route, it's a little bittersweet, but still optimistic. Then at the very end we see [[spoiler:Kuroha]]. [[spoiler:In Chapter 18, Kuroha immediately brutally murders Seto, Kido, Kano and Ene on page before Mary resets the route.]]
* MoralEventHorizon: Route XX Shintaro arguably crosses it when he [[spoiler: chokes Ene to death when she was just trying to help him.]]
** [[spoiler: Kuroha]], when he [[spoiler:murders everybody.]]
* NightmareFuel: [[spoiler: Kuroha]]'s expression in the [=MekakuCity Records=] crossfade PV.
** Outer Science in general.
*** Everything about [[spoiler:Kuroha]] for that matter.
** Mary, screaming silently at the end of ''Outer Science'' [[spoiler:as her hair falls out, forms into snakes and turns black and scales grow over her skin.]] Seeing the series' most {{Moe}} character like that is... just upsetting.
* OneTrueThreesome: The original Mekakushi Trio, Kido, Kano, and Seto.
** Shintaro, Ene, and Konoha are sometimes shipped like this too due to their canon interpersonal relationships. Also popular is any shipping between the One True [[UpToEleven ''Foursome'']] made up of Shintaro, Ayano, Haruka, and Takane, affectionately known as the "Yuukei Quartet" by fans.
* TheScrappy: Hiyori is seen as this by some.
* TearJerker: [[spoiler: Ayano's suicide]], and Shintaro's reactions in ''Toumei Answer'' and ''Lost Time Memory''.
** And then ''Ayano no Koufuku Riron'' came along and made it even worse.
** [[spoiler: Challenge. Watch Yuukei Yesterday and then Outer Science. Or just read the manga up to Haruka's death and try NOT to cry a single time. If you win: good for you. If you lose: congratulations and welcome to everyday life of the fandom ]]
** The Kagerou Days time loop, and its affect on Hibiya in Otsukimi Recital.
* ViewerGenderConfusion: Kido. Even Jin was confused with her gender!
* WhamEpisode: ''Lost Time Memory'', with its reveal that [[spoiler: Ayano had an eye power, and Shintaro may have inherited it]].
** ''Ayano no Koufuku Ririon'''s reveal that [[spoiler: Ayano was the sister figure to Kido, Seto, and Kano, and the original creator of the Mekakushi-dan]].
** The [=MekakuCity=] Records booklet, since it reveals that [[spoiler: everyone actually came {{Back From The Dead}} because of their eye powers.]]
** '''''[[FriendlyTarget OUT]][[FamilyUnfriendlyDeath ER]] [[KillEmAll SCI]][[EverybodysDeadDave ENCE.]]'''''
** ''Anime/MekakucityActors'' episode 11. [[spoiler: Not only is Shintaro's ability revealed to be the "Recording Eyes" ability, but he's been with it since he was in the womb.]]
* WhatCouldHaveBeen: Jin stated in an early interview regarding Hibiya's background (before he was properly introduced in the novels) that he would be ChildhoodFriends with Hiyori. He also mentioned that Hibiya's quite popular in school, his only downfall being that he can't get Hiyori to notice his feelings for her. By the time he's properly introduced in the novels, however, with the exception of his unrequited crush on Hiyori, his background is completely rewritten.
** Konoha was originally supposed to be a girl.
** Jin originally wanted to name the series Mekakucity Project, which was evident when all of his major [=KagePro=]-related albums are called Mekakucity ______. However, [[MagnumOpus Kagerou Days]] [[ToughActToFollow got too popular]] and so Jin was forced to name the series after it. He eventually got his way in [[Anime/MekakucityActors the anime]].
* WorldOfWoobie
* WellIntentionedExtremist: Though Ayano obviously always meant well, and everything she did was for the sake of her friends and family, many of those things were... not very well thought out. [[spoiler: Such as pulling off her suicide stunt when ''Kano was right there'', and just in general getting him involved in a situation that ultimately made his already poor emotional health even worse. Not to mention Kido and Seto who also suffered from losing her. Ayano was so concerned for her adopted sibling's lives that the emotional impacts her death would have on them apparently slipped her mind.]]