My Guardian Spirit is a Slime

In a fantasy world where people perform supernatural acts through being possessed by spiritual guardians, a lonely girl who was abandoned in the Forsaken Zone- a massive country-sized landfill, discovers a small gooey object stuck to her hand. The slime- the most weakest spiritual being according to records throughout millennia, had chose her as its vessel. Together, they make it out of the Forsaken Zone into the city, where they prove their power against all sorts of warriors and villains.