The beginning of this clip features an amorphous mass of slime that needs to be fed human semen first before it can evolve into its next life stage - the slime girl. Having reached this stage, the owner can then engage in any type of desired activity with the slime girl. You can see the huge personality differences between the green and red slime girls. The green one - she's rather exasperated at how perverted her owner is, and how many crazy and unorthodox sex positions that she has to get into just to please him. As for the red slime girl - she's a bit more innocent, perhaps even naive, and is more in wonder than anything else that her owner has a thing for her feet. Nevertheless, the relationship is always completely symbiotic - the male human gets what he wants, and the slime girls can continue living (and yes, they do enjoy the sex part too).