#i don't just accept or reject theories based on the literal mechanics of the world

[pricechecktranslations]

Is it possible that Allen and Rilliane are the reincarnation of the twins taken from Marina Lucif? They'd be Irregulars like Hansel and Gretel, and it would be poetic for them to wind up in the same family. I know Rilliane and Allen were supposed to be Hansel and Gretel, Irregular twins, but what if instead of outright changing fate she just altered it slightly. Since Allen and Rillane were supposed to be Irregular twins, fate adjusted accordingly and gave them the Lucif twins souls instead.

I suppose it's technically possible but there's never been anything saying one way or the other. The biggest problem I have with this theory is that this implies Allen and Riliane have lives previous to their lives as Allen and Riliane--that is, even if they only reincarnated the one time before (which, if Hansel and Gretel were fated to reincarnate through the Gluttony era, why not the Lucif twins? Why would they not also have multiple identities down the line?), that is still at least one identity that is never so much as touched on during Master of the Heavenly Yard, despite the novel featuring/mentioning all of their other identities (as well as all the identities of other characters who have reincarnated or otherwise changed form throughout the series).

More simply put, there are times in the story where this would have been relevant to mention, and the fact that mothy didn't at any point makes me think it's not the case.

(and it's not guaranteed that the Lucif children were Irregulars. Marina's husband took them--maybe unbeknownst to the Senate they were naturally conceived. there's not a lot of detail to go off of here.)

I also don't think "changing fate" is a. mechanic? In the way you're thinking of. Like, the point of that phrase is just "these twins were supposed to be the bodies for Hansel and Gretel. Instead Gretel ended up somewhere else where there could be no Hansel, and so Allen and Riliane had nothing to do with Hansel and Gretel despite looking identical to them". I think of it more like a computer glitch, something to hand-wave using the Kagamines for both sets of twins, not some prescient force able to make "adjustments".

This would also imply the existence of another set of Kagamine twins that the Lucifs were "fated" to reincarnate into, if they were Irregulars along this line, which is frankly getting into ridiculous territory.