Sebastian sensing souls and the Bizarre Dolls at Weston
All right, that's enough about tradition and Weston rules for a while. Let's talk about the supernatural. (Hella spoilers for chs 67-84 again, with bonus spoilers for ch 60.)
Recall from chapter 60 that the Undertaker makes his first round of Bizarre Dolls by attaching artificial records to the end of corpses' cinematic records. Those Dolls seek out and destroy humans because they instinctively desire souls to complete themselves.
The Bizarre Dolls in the Weston arc are a little different. Undertaker creates these Dolls by attaching their own "episodes," their hopes and dreams for the future, to the ends of their cinematic records. (In the original Japanese, Sensei uses the kanji 素材 (sozai), which means "raw materials; subject matter." However, the kanji is accompanied by the pronunciation "e-pi-so-do," so take that as you will.)
Even with more genuine records, the Dolls of Derrick Arden and his friends attack humans when given the chance.
We've known for a while that Sebastian can detect souls at a distance, but it's not very clear how Sebastian's soul-sense reads the Bizarre Dolls. During the Campania arc, he never says he can't detect the Dolls. He just says, "It is a being I do not understand" (ch 52 pg 34).
Even so, I think it's interesting Sebastian never said anything to Ciel about soulless things at Weston before the midnight tea party.
Maybe he could sense all of the Dolls perfectly, knew exactly where they were right away, and didn't say anything because Ciel never asked. He's been known to pull that shit before.
But maybe the Dolls are completely invisible to his soul-sense. That would explain why he never found Derrick before his corpse waltzed into the tea party.
Whether or not he can detect the Bizarre Dolls without seeing them, he must have been keeping some suspicions from Ciel. There's this Vice Principal walking around, interacting with Sebastian, running the school, who’s been dead the whole time. Sebastian must have noticed something was unusual about his soul.
The Undertaker calls the VP Agares Doll his "masterpiece" (ch 84 pg 14). Not only is this Doll able to masquerade as a complete human, unlike the other Dolls, it never attacks humans to take their souls.
If the Agares Doll has such a near-perfect soul that it doesn't need to seek human souls to fill its void, that implies the corpse itself seems finds the episodes an acceptable soul substitute. Even the Doll seems to be aware that it is running on episodes (ch 82 pg 13):
When all is said and done, the Undertaker is getting scarily good at recreating something approximating a soul. I wonder whose soul he's hoping to recreate...