Umm, what about a fairy tale theme? Or just a literary one, like, in general? Famous love stories? For the morbid, doomed couples?

Or the myth of [...] Persephone? There could be an "earth" and an "underworld" and everyone could wear togas or whatever? But like, Greek gods are done to death so maybe not.

Also, I think matchmaking with divination is cute and on trend.