There used to live a species known as demons, these demons are beings capable of being immortal and are able to use blood demon arts that are different between each demon. The king of demons is Muzan who has been created through a medicine the blue spider lily

modern time

due to modern technology the blue spider lily have been added in medicine for pregnancy and now quirks were born but it is unexplained on why quirk users don't burn on sunlight and have no bloodlust

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