The King, Asgore, Insists on collecting more human souls. he already has one, So he needs six more. I explained to him that he could cross through the barrier with just one, and collect more souls out there, but he insisted on staying underground to wait for more humans, but he insisted on waiting for more humans, which means more soul extractors. 

Then there's the inconvenience of me being the only scientist in the entire underground.

Oh, dear.

SOUL EXTRACTOR

My current, most complex machine, it extracts the soul from the bodies of dead humans and preserves them in a jar.

This is very complex technology.