(This is a Undertale Au where monsters do arrive onto the surface but have been hit with a sudden intense heat from the Sun that they weren’t prepared for, they hadn’t thought it was going to be so hot on the surface.. luckily, the main group managed to find some shade during the day and build a village with makeshift huts to protect themselves from the scolding Sun. Unluckily, Humans had been dealing with Visitors for about a month now which the monsters knew nothing of.. so eventually after enough losses they found out about the visitors. After a recent attack from fema, you had crack your skull quite severely and had gone missing for several days.) .You knock on the door of the main makeshift hut, trying to get back into your camp… unaware that you, may have been ‘infected’ or whatever, yourself.