Another soulmate idea cause why not
Music!!! Basically people will have their own unique music, be it in their head, their soul, whatever. And whoever else harmonizes perfectly is the other's soulmate.
Sometimes the music has words, other times its just soft humming. Sometimes it's hard rock other times it's lazy folk song.
Depending on how the logistics work is could see some pretty angsty scenarios.
Outside of relationships: imagine random character is deaf, hard of hearing, sensitive to sound? Imagine if character has been memories related to a type of music that is their own or someone they know's soul song?
Imagine the music industry and how it's affected.
Imagine, if this is an au where everyone can hear everyone's soul music, BAD PEOPLE luring in others with their soft tunes? Or, in aus where the songs are private, someone faking their soul song with an mp3 or something?
Imagine in certain communities or groups where specific kinds of music is frowned upon yet a family member or two gets such a kind of soul song?
For the sweeter versions - Romance, sexuality, and aesthetic feelings ARE impacted the the music, and as well, the music is impacted by the person's preferences. Orrrrrr, horror version - a person's song reflects very minimal about them because a soul is a soul with core features. A human can drastically change but by then their song has been made and mirrors a version of themself lost to time.
What if someone's song blends with MANY people? Not soulmate level harmonizing but close enough to get people comfortable and interested? And the opposite. What if someone's tune is so grating or horrific that it makes others cover their ears and stay far away, maybe making assumptions on the characters personality just based on their song?
Being a concept of course people can do with this soulmate au as they like. Maybe the songs CAN change with the person but stay unique enough to them that they keep only the one soulmate. And if their song changes perhaps so does their soulmates for the harmonizing.
Maybe you want to make this idea scientific and relate it to the heart waves, sound waves, the abstract invisible waves that give people their sixth sense.
Maybe you just want it to be unserious and fluffy with no explanation at all.
