Honestly? Stop trying to make them 'unique' in the sense of a brand new plot device and just... read the myths again. The Ovid version, the non-Ovid versions, the fragments. Apollo's not just the golden boy sunshine god—he's a god of plague, of sudden violent death, of purification through violence. Hyacinthus isn't just a pretty boy who got hit with a discus; in some tellings, he's a pre-Hellenic deity of vegetation who gets reborn. A 'unique' pairing would lean into that darkness. Make Apollo aware, on some level, that he's enacting a cycle of death and rebirth he can't control, that he's both murderer and mourner eternally. Or flip it: Hyacinthus knows. He's seen it in dreams, knows the discus is coming, and chooses it anyway as an act of devotion or a bid for apotheosis. That tension—between fate and choice, divine function and personal agony—feels fresher than another coffee shop AU.
Most fics just transplant modern relationship dynamics onto them, which is fine for fluff, but it strips out the inherent tragedy and weirdness of their myth. Let them be ancient and strange. Let their love be incomprehensible by human standards. That's where the interesting stuff is.