Let’s unpack this scene, where Sebastian explains how Agni acquires superhuman strength (ch 18 pg 23).
I checked the Japanese to see whether Sebastian really said, “Something we could never obtain…” because sometimes fan translations are imprecise, and this “we” is critical to the interpretation.
The original is “私達には持い得ない.” I totally agree with the fan translation on this one. Not only is “私達” (watashitachi) definitely “we,” but it’s bolded in the original. We are most entitled to play with “we.”
So who is this “we”?! Is Sebastian referring to the people in the room? To all demons? To himself and Ciel?
There is no right answer; that ambiguity is part of the joke, which is why get this panel of sly Sebastian looking all slyly at Ciel. Soma and Lau are in the room at this point, but only Ciel and the reader know about Sebastian’s true condition.
Soma and Lau must think Sebastian means that Agni is incomparably pious, and therefore
Sebastian holds his hand over his chest suggesting his “we” refers to all demons. Surely demons cannot achieve a power granted by love and faith in god. Demons oughtn’t love a god who cast them out of heaven. They needn’t have faith in one either.
But what about Ciel? You’d think that since Ciel has proof positive of the existence of religious figures, he’d have an easy time believing in a god.
But what would be the point? Ciel’s fate is sealed. He has turned his back on the light and charged into the abyss. Even if he could find love and belief in a god, forgiveness and redemption is beyond Ciel’s reach.
“The price to cross the river has already been paid.” Ciel will be crossing the river.
No wonder Ciel’s expression says, “Rub it in, why don’t you…”