>Appearance: Taka onna appear as ordinary, homely human women most of the time. But they have the power to elongate their bodies and grow to several meters in height. Like other brothel yōkai, they are rarely seen outside of the red light districts, but are fairly common yōkai nonetheless. Sightings of these yōkai peaked during the Edo period and continued up to the post-war period—the time when brothels and yūkaku (“pleasure districts”) were at their height in Japan.
>Behavior: Taka onna are frequently spotted peering into the second-story windows of brothels and homes where romantic liaisons are taking place. Their activities are generally limited to peeping into windows. Though they rarely attack humans physically, taka onna do enjoy scaring and harassing both men and women who frequent the pleasure districts, jealous of the physical pleasure they were never able to know in life.
>Origin: Taka onna were originally ordinary women who were too unattractive to marry (or to find work in the red light districts which they haunt). Through jealousy, they became twisted and corrupted, and transformed into ugly, malicious monsters that prey on others’ sexual energy.
I guess Mega Froslass is basically Yuki-onna + this monster.