"Sometime after being sealed Underground, monsters began to suffer from widespread infertility, and their numbers began to dwindle. About a decade after the son of Asgore and Toriel had been stillborn, a human fell into the Underground. This human, named Chara, had the SOUL TRAIT of LUST, and soon after entering the Underground began murdering all monsters that crossed their path for their own sadistic pleasure. Eventually, this Human was killed and their SOUL captured."