[LyricalAura]

Originally Posted by Shiro Kaisen

Shannon, having faked her death at the First Twilight, is alive and is allowed into Eva and Hideyoshi's room by Eva and Hideyoshi. They knew about the fake death plan, and that's why Hideyoshi didn't say anything about her being alive, as they assumed Shannon was in on it because she was in the shed! She kills them, and hides under the bed!

As far as I've been able to determine, the murderer doesn't particularly go out of their way to create closed rooms, and doesn't seem to have a problem with just leaving bodies lying out in the open either. So if a closed room appears that would require the culprit to endanger themselves in order to construct it, we should instead suspect that the closed room was not created by the culprit alone. In the case of the EP1 second twilight, the closed room is easy to explain if it was constructed after the murders occurred by people other than the culprit.

It is almost certain that Kanon faked his death at the fifth twilight with the help of Kumasawa and Nanjo. We can walk that theory back to get a picture of how the second twilight occurred.

Spoiler for Clues, long:

• Supposedly Kanon and Kumasawa went to get shears from the basement storehouse to break into the guest room. But this would put them right next to the boiler room where Kinzo's body was burned, which they somehow totally failed to notice even though Genji claimed the corpse had been burning for a while.
• Because they supposedly didn't find Kinzo's corpse until after the 2nd twilight, nobody should have known about the stakes being used to follow the epitaph gougings ahead of time, or that the fourth twilight was already finished. In that case, even if Kanon had a stake and came up with the idea to follow the epitaph, in order to fake his death he would have needed to pull off a head wound, not a chest wound. In that case, the explanation of "pulling the stake out after being attacked" would have been impossible, so having a stake would have been useless. So it's reasonable to theorize that Kanon and Kumasawa already knew about Kinzo's corpse being burned and staked, but kept quiet about it.
• Since Kanon could not have planned to fake his death in the way he did without knowing ahead of time that Kinzo had been staked, and since the stakes are likely to have come from the same place, we can turn around and conclude that Kinzo was staked precisely so that Kanon could fake his death with a stake.
• However, if the burnt corpse wasn't originally staked for the fourth twilight, that means there's no reason for the culprit to have burned it. Therefore, the corpse must have been both burned and staked by the servants. This would explain why Kanon and Kumasawa didn't report finding the corpse when they went to the storeroom.
• The letter at the third twilight serves no purpose other than to reinforce the belief that the epitaph is being followed. It also never appeared in any other episode, so we can determine that it was written because of specific EP1 circumstances. For that reason, we can tentatively connect it to the faked fourth and fifth twilights. This is useful because...
• It is impossible for the magic circle on the guest room to have been painted in the short time Kanon and Genji were supposedly away, which means both of them lied about it and probably painted it themselves. This makes sense because both of them were implicated in magic circle painting and pranks by Gohda's notebook. The only reason for painting such a thing is to give the appearance that magic has taken place, which ties it to the faked third through fifth twilights. Genji is now implicated in the fake death conspiracy as well, which lines up with him lying about how long it would take Kinzo's corpse to stink up the house (we can tell from EP4 that it takes two hours at most).
• Adding additional magical elements to the second twilight crime scene should have been unnecessary with the bodies already staked. Therefore, it makes more sense for all of the magical elements to have been added at once, including the stakes. This is not particularly difficult since the servants have the stakes.
• Eva's body was found lying face-up on the bed with her shoes still on, which contradicts the prior scene showing Eva and Hideyoshi having an intimate moment in bed. This strongly suggests that she was actually outside the room when she was killed, and that she was carried back and posed.
• However, based on EP2 and EP4, the culprit doesn't seem to particularly care about having the second twilight victims together, so there's no reason for them to drag Eva's corpse around and pose her. Therefore, the posing must have been done by the servants afterward, which is in keeping with their other actions to create the illusion of magic. The shoes speak to a lack of attention to detail, so the open jar of soap in the shower would tend to confirm that Hideyoshi really was killed there.
• Since the culprit wouldn't deliberately endanger themselves to create a closed room, we can just conclude that the chain lock wasn't set after Hideyoshi was killed. The servants were building a magic illusion, so it's in keeping with that to cut the chain and then pretend that it had been set.

So the short version of the theory is: The servants and Nanjo discovered Eva and Hideyoshi's bodies, at which time the chain was not set. Since it looked like the murders were going to continue, they created a plan to trip up the culprit's accomplices (by altering the second twilight crime scene and setting up a weird magical incident) and fake Kanon's death so he could keep an eye out for the killer. This plan explains all of the details of the second through fifth twilights.

Of course a theory where all of the servants are the culprits is also possible like this, but I think most people would agree that it would be incredibly unlikely.