Fallen Flowers is an AU where humans who fall into Mt. Ebott maintain their SOULs, but they do not maintain their human forms. Instead, they take on the form of a monster. The mages who sealed the barrier added this curse in order to prevent monsters from using seven human SOULs to break the barrier. Humans can be differentiated from monsters in the Underground by the flowers that grow out of their monster form, which represent their SOULs. However, these flowers wilt over time. When all the petals from these flowers have fallen from a human, they will cease to be human.
The monsters of the underground are divided between the Guardsmen of King Asgore and the survivors, who take refuge in resistance groups. The Guardsmen are often described by survivors as "soulless", and they are a threat to survivors due to the fact that monsters have been disappearing under their reign.