Long ago, two races ruled the earth, humans and monsters, they lived in harmony working together to make beautiful symphonies, one day war broke out, and after a long battle, the humans were victorious. They sealed the monsters underground with a spell….

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Souls

In this au would have their own symphony and produce music, the music tells the story and emotions of the monster/human and it has become a core part of the culture.

How strong the souls music is shows how powerful the monster/ human is, boss monsters tend to have strong powerful pieces (toriel or asgore) but the more meek monsters may have a simple quiet tune to their soul.

Because music became a huge part of culture with both humans and monsters they worked together and their souls created glorious symphonies as their souls worked in harmony, however humans have the most variety to their music and thus over time they felt less need to work with the monsters and insolated themselves, and then eventually war broke out and know the story.

Soul sounds

Integrity: high string

Perseverance: low string

Kindness: high wind

Bravery: high brass

Justice: low brass

Patience: low wind

Determination: percussion

Monster souls: keyboard.+ Soul sub type

Soul subtype: the monster soul + a human trait

Some monsters, typically boss monsters or simply the powerful ones, and the wizards of the past could control the flow and sound of their soul song, the only known monsters to be able to do this are asgore and toriel (and genocide rout sans) and later frisk, and that one temmie. Some monsters but not all monsters have a soul subtype, only strong monsters have the ability to do so much like the ability to control the flow of their music.

However, a monster or humans sing can be changed depending on the mood their in, however that really only effects the tone of the piece, however it can be changed more fully by changing your morals and who you are as a person, (changes that would show through sans, undyne, flowey, alphys, and genocide frisk.)

Monsters with the soul subtypes: sans, papyrus, toriel, undyne, mettaton, muffet, asgore, shopkeeper temmie after college

Exceptions: amalgamations, flowey

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World build changes

Not much really changed in of the world build, however grilbys now features a karaoke singer.

Outfits are more based about band conductors, amplifying their souls music, and the famous concert black(kind of) and professionalism, monsters in this au really like to perform and show off their souls music and the underground gives people the opportunity to do that here, now that social media is a thing and mettaton isn't the only famous monster underground, however much love humans the music culture is starting to fade out as they find new sources of entertainment like talkshows and such.

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Personality

Monsters in this au are either very friendly or really edgy and there is no in between, but most are on the friendlier side and are generally more sympathetic and ive of each other as music and the fact music literally comes from the soul brings emotions and sympathy out of others and so their generally more caring of each other and new people the community now is built more on trust than it is consumerism, however is they were to meet someone with no soul song it would definitely scare them.