how about possession AU where instead of being evil spirits its just ghosts of long lost lovers who want to finally be united (and maybe bone down) and choose g and sid for *handwaves* reasons. and instead of being all ominous it just results in the team finding the two in compromising positions, talking like some sort of bodice ripper romance characters. also g would totally be possessed by the lady ghost. because imagine him swooning into sid's arms.
om g LOOOOL okay tbh when i first read long lost ghost lovers I immediately thought of a ghost who latches onto sid because Sid looks like his lover, and he thinks that his lover has finally come back to him (his lover died - either killed by angry townsfolk or at sea, i haven’t decided yet), and the ghosts sees geno as someone he must get rid of