Kogasa was originally an eggplant-colored umbrella, but was never sold as that color proved to be unpopular. After remaining unused for one hundred years, she became a kasa-obake, or umbrella ghost, a type of monster from Japanese folklore. She tries to surprise humans, but doesn't actually want to harm them.
She first appears in Undefined Fantastic Object, where she has no real connection to the plot. She attempted to scare the heroine twice, but it seems that seasoned youkai hunters don't find her very frightening.
In Ten Desires, after finding a home in the graveyard adjacent to the Myouren Temple, Kogasa attempts to scare the Buddhist magician Byakuren Hijiri, but finds that Miyako Yoshika is invading her turf. After attempting to convince the heroine to defeat Miyako, Kogasa herself is defeated.