!Per wiki policy, Administrivia/SpoilersOff applies here and all spoilers are unmarked. Administrivia/YouHaveBeenWarned.

!Manga
* The manga opens with the shadowy image of a crying girl, and a tale of a child named Yuuko being [[HumanSacrifice sacrificed]] to protect the school. We then learn more from a vision that Teiichi has while talking with Yuuko: Yuuko was not only sealed up in a basement, but also had a broken leg - she died scared, alone and in pain, pleading for help all the while. The vision is somewhere between chilling and [[TearJerker saddening]].

!Anime
* Episode 4 gives us our first proper look at [[ShadowArchetype Shadow Yuuko]] as she stands over a sleeping Kirie, displaying a full on SlasherSmile full of dagger-like teeth.
* Episode 5, while mostly lighthearted fun, has a really dark {{Mind Rape}}-ish segment that feels more in line of ''Anime/PuellaMagiMadokaMagica'' or a [[ShadowArchetype Shadow confrontation]] from the ''Franchise/{{Persona}}'' games.
* Episode 6 re-introduces the HumanSacrifice plot point above. Yuuko had made up a monster that was terrorizing the school as part of a [[BatmanGambit gambit]] that ends up [[GoneHorriblyRight more effective than she'd intended]]: she's offered up as a sacrifice to the monster, with people she thought of as friends willing to go through with it to save their own skin - and it wasn't even out of malice towards her...
* Episode 10 is equal parts heart-rending and horrifying: Teiichi is trapped inside Yuuko's body via memory flashback and ''[[ForcedToWatch made to experience]] Yuuko's "sacrifice"'' - being thrown into a filthy pit and left there to slowly go insane and die of starvation, unable to move the entire time. Not long after, Teiichi decides to [[UnPerson block her out of his mind]] and stopped seeing her, slowly forgetting about her before long. One is left to imagine just how traumatizing that was for him.