This started out as a regain thing but now it isn't but I'm going to ask here anyway because it has to do with using completed crystals for things and maybe someone else will have a similar idea:

So in Pandora Hearts world, there are two kinds of Contracts with the demons Chains. There's the one Kevin had, wherein the Contract was etched into his flesh and he was driven to kill a lot of people, and there's the one the Pandora people had, where the Contract was displaced onto a special mirror pendant so the Contractor could use the Chain but not have to feed it in return. We have zero information as to how the mirror is special, just that the guy who started Pandora figured out how to make it work, so probably there's some weird canonical magical woo to it.

Say my cast worked some further magical woo in which Gil's canonical ability to access the Abyss and Kevin's canonical ability to march right into the center of it instead of getting eaten were combined, and though they couldn't get home they could at least reach the Abyss itself, and thus have access to Chains. Could Kevin use one of his completed crystals in place of one of those special mirrors, and make a non-deadly Contract? Since the crystal is already aligned to him and full of his emotions, it seems like it would be an excellent substitute for "let me chew on your soul".