A Byobu Nozoki is a particularly perverted Tsukumogami that manifests after a folding screen has existed for many years and hidden the acts of many sexual activities, resulting in a spirit that resembles an impossibly tall humanoid in white robes who enjoys peering over the side of screens whenever people are engaged in sexual intercourse.
While not a harmful spirit it is nevertheless a creepy and startling creature and like many yokai is mischief-prone in nature, it also feeds off sexual misdeeds - which were part of how the creature came into existence in the first place.