Lit.: "the last day 20"

An unlucky day in which one ought to take special care of themselves to avoid misfortune!

This day is said to be the only one in which the man-eating youkai "ippon-datara" is able to move freely! The ippon-datara is a one-eyed and one-legged youkai, somewhat similar in appearance to a karakasa-obake. In fact, half of Kogasa's overall concept is inspired by the ippon-datara. The ippon-datara is said to be connected to blacksmithing, in particular to a kind of furnace called tatara, as it was said one of the blacksmith's legs would atrophy from stepping on the bellows always with the same foot, and one of the blacksmith's eyes would go blind from looking into the furnace. This is part of the reason behind's Kogasa's heterochromia (one of her eyes is red), part of the reason behind the fact she's usually shown standing on one foot (although this is also because karakasa-obake only have one leg —the umbrella's handle), the reason behind her surname, and the reason behind her being a capable blacksmith in canon.

Everyone is only scared of this guy over here...

But I'm more frightening than them!

Tatara Kogasa-chan being jealous of her own umbrella