Gensoukyou:Kogasa Tatara

Background
A particularly wealthy, middle-aged woman once had a purple umbrella that was quite well-crafted. She would carry it around everywhere, showing off the quality to her wealthy friends. The umbrella was not well-cared for, despite this. The woman never cleaned it, even after it got dirty from the rain, and even the quality could not keep it in good condition forever.

Eventually, the woman's friends took notice and panned the lady about her dirty umbrella. They even called it tacky, and out of style. Being quite vain, the woman replied with a "harumph" and promptly tossed the umbrella away.

So it sat where it was tossed by the roadside for a good few days. Nobody ever came to pick it up, as the color was indeed going out of style. Eventually the wind swept the umbrella away. Unwashed, unwanted, and undesired, the divine spirit within the umbrella became angry at its treatment and misuse, and became a youkai.

Being a youkai, Kogasa desired revenge on humans. she changed her form, giving the umbrella she carried a ghastly eye and a very long tongue, and set off to find the woman who owned her.

It didn't take very long for Kogasa to find her past owner (as the woman walked around a lot and Kogasa remembered where she lived) That night, Kogasa burst into the home and wailed "You'll pay for having abandoned me!" The old woman was so distraught by the surprise that she promptly fainted.

Kogasa then giggled and found the reaction particularly hilarious. So from then on, she decided she would get revenge on humans by scaring them. She would go where the wind took her, and get the jump on humans, screaming "Boo!" and other simple techniques, but that was almost always enough to spook the victim anyway, mostly because of the fear youkai brought in general.

However, as time passed Kogasa and other youkai began to come under skepticism, and were in general viewed with less fear. Humans would sometimes not be afraid of Kogasa's surprises, instead laughing at how goofy she looked, thinking she was just a dressed up human child. Kogasa would become depressed when this happened, and would attack humans who did this as a result. This seemed to scare them away easily enough, as they didn't expect she was an actual youkai, but it never gave Kogasa the same thrill.

Eventually, Kogasa would be swept away by the wind into Gensoukyou, where she continues to surprise people, but since this no longer works very well (hardly anyone is ever surprised by her now), she has begin to question her purpose in life, considering perhaps going back to being a normal umbrella, or taking up a different profession.

Personality
Kogasa is generally cheery and carefree, going where the wind takes her, and surprising people when she sees them coming. Her grudge against humanity has worn away over time, so she is actually quite friendly to humans when she is not trying to surprise them.

However, Kogasa is easily depressed. Her mood will turn sour when she fails to surprise somebody, becoming quite gloomy and pensive. She's prone to attacking people when she is depressed, and generally seeks attention from others, not wanting to be forgotten again. In addition to seeking attention, Kogasa also despises not being taken seriously, despite how goofy she looks. It may be in your best interest to feign surprise to keep her happy, as she is much more amicable when she isn't depressed, and she can't really tell the difference anyway.

Kogasa dotes often on her true purpose, and the purpose of other youkai. Deep down she really just wants to be desired by others, either as a "scary youkai", a friend, or helpful in some regard.

Kogasa isn't very smart, but supposedly ignorance is bliss, which seems true considering how happy she is despite it all.

In a way, Kogasa is just a youkai child, and generally acts much like a child would.

Power/Combat
Kogasa does not have many actual powers, but instead of eating humans, she feeds off spirit, which she will do when someone is surprised by her.

As such, her profession is scaring people. Unfortunately, she is not very good at this. Her surprise techniques tend to consist of trying to jump out at others and scream "Boo!". To make matters worse, she isn't very hard to spot when she is "hiding", as her goofy, large umbrella and bright colors tend to give her away, even late at night.

However, because she's likely attack out of desperation when someone isn't spooked by her, it is probably a good idea to at least feign being surprised.

Kogasa can change her appearance with some effort, using this ability to become "scarier", but sometimes this backfires and she looks even more goofy then before.

Myouren Temple
Kogasa is acquainted with the people residing at Myouren Temple, as the graveyard behind it is a good place to spook people. However, she isn't affiliated with the Myouren Temple.

Hakurei Shrine and Moriya Shrine
Kogasa visits both of these places regularly. While the Hakurei Shrine Maiden only tolerates her (like other youkai that visit), she doesn't get along well with the Moriya Shrine counterpart.

Trivia
-The backstory and personality are already clearly defined in canon, so there wasn't much I could do aside from flesh it out.