In "Stardust", only Septimus’ soul goes to Hell. Why?

I think it's because he was the only brother that killed other people while his brothers only ever killed each other, iirc. Fratricide for succession seems to be a norm or a tradition in their world, which is why it seems the killed brothers held no ill will to their fellow brothers, the late King being unbothered his children's fratricides and his own, and the town having an inn called "The Slaughtered Prince". So murdering each other wasn't an evil act, it was just a way of life for them, and Septimus killing other people was not.

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