Cho-Ru

From NexusWiki

"The Cho-Ru spirit is believed to be an ancient ghost-like being. Scholars believe that after an extended period away from their corporeal bodies, the strongest willed ghosts become Cho-Ru. These spirits are believed to possess near, if not complete, immortality and immense magical capabilities. Cho-Ru spirits have never actually been documented, but some believe that they are responsible for inexplicable phenomena like weather and vanishing items. Still, many others doubt the existence of such a strange entity."

-Librarian Pond

Cho-Ru spirits are the in-character explanation for floorsweeps, although there have been rumors that there is more to the legend.