Accidental Innuendo: Miyako ended up lost in Minakami village while looking for her boyfriend, Masumi. She ends up getting strangled by his hostile ghost, and her final diary entry says, "He came...". And even her words when defeated as a ghost are, "You finally... came...". Considering how hard this phrase would be to work around from Japanese into English, the translators probably realized the implication and just shrugged their shoulders.
Mayu can be interpreted in a number of ways depending on the choices the player makes in the game. One thing for certain is that the game makes it ambiguous as to how much Sae has influenced her personality, or if she was like this to begin with. While Mayu is weak to strong spiritual influences and scared of being abandoned by her sister, there are also indicators that make her appear manipulative. The Official Fanbook states that Mayu purposefully fell down the cliff, to injure herself badly enough that Mio would be guilt-ridden enough to never leave her side. The remake added Event Flags that ended up influencing which ending the player obtained and how Mayu's character would turn out, making the whole situation even more ambiguous, since each of them showed conflicting messages.
Sae may be someone who genuinely cared for her sister, hoping that Yae would make it back in time to rescue her when she fell behind in the forest. Her diary definitely shows that she was close to her sister, and loved her, but with the way she was raised, her mind was still set on the ritual. And she can be seen as someone who was so obsessed with performing the ritual and 'becoming one' with Yae that she completely disregarded her feelings on the matter.
Incest Yay Shipping: Given the heavy undertones of twincest and unnatural obsession twins have with each other in this game, it's no surprise that they and Mio/Mayu have quite a fanbase.
It Was His Sled: Mio must kill Mayu, not the other way around. This used to be the big plot twist of the game, since the latter was how things kept being portrayed. It wasn't until Chapter 8 that there's a note mentioning that the village considers the second-born to be the 'older' twin, since it was believed that the 'older' twin would let the 'younger' twin be born first, making everyone realize what was actually going on.
Les Yay: Mayu and Mio have their share of it, particularly on Mayu's side.
Most Annoying Sound: The sound the camera makes when the spirit charge is maxed out, which only gets worsened by the Butterfly lens that adds a second charge on top. It almost makes the player not want to charge up their shots, just to avoid that sound.
Narm: Sae loses her creepiness when she stumbles forward and flails her arms around in-battle.
The Scrappy: Mayu gets called one because she has no means to help out when hostile spirits are around. She also forces the player to spend half the game escorting her, and she's not invulnerable. And there's also the fact that she keeps disappearing, meaning the player has to go back and look for her, potentially rescuing her.
Squick: The shot of Mayu's accident. Her leg is lying at an odd angle.
That One Boss: The second encounter with the Kiryu Twins in the Doll Room. The difficulty comes in the Doll Room being a rather small area, so there's not a whole lot of room to move around in and it can be difficult to avoid getting hit.