“Oh yeah, she's that one shrine maiden who goes around slaughtering everyone who bothers to exist.”
Reimu Hakurei, also known as Ganondorf, is the only worker at the Hakurei Shrine, a financially suffering, godless, pointless shrine in Gensokyo, and also the only person (aside from Chuck Norris) to ever believe that it's not butter.
Born in The Gerudo Desert, Reimu spent most of her early life gardening and shaving her unsightly armpits. Although this life sounds fascinating and likable, she actually struggled to find a boyfriend, or any friends for that matter. She decided to travel afar to find someone who would not judge her by her bodily hair. Said journey brought her to Gensokyo, where, to her dismay, 99.99999999999999999% of the population is comprised of females. It was at this time that Reimu met Marisa Kirisame, a witch who never has anything to do but mug people and then steal their stuff. Both being social outcasts, Reimu and Marisa hooked up and became best friends.
One day when reading a book that Marisa had stolen from some pajama-wearing librarian Reimu discovered that a remedy for unsightly armpit hair had been hidden away in the mountains above her shack of a shrine. She immediately set of to find the potion but was stopped by various monsters, demons, angels, unicorns, succubi, kappa and elves, all simply referred to as youkai. Reimu, defeated, went back to her shrine in shame. She was moping about when she found a magical off-color yin-yang orb. She equipped the orb and used it like a kickball to kill youkai. With this as her weapon she ascended the mountain.
After finding an entrance to the demon world in a cave, Reimu fought an Archangel named Sariel using only her kickball and a stick she had found earlier, and won. Reimu kept searching the mountains and this time found a route to hell (of all places). Curious, she descended into hell and fought a master swordsman (or woman, nobody really knows) named Konngara. Reimu emerged the victor once more by blinding her opponent with her armpit hair before striking him/her in the face with her yin-yang.
After her exploits in hell Reimu continued her search for the armpit hair remedy in the surrounding forests and mountains of Gensokyo after a short vacation in Hawaii. While in Hawaii she captured a giant turtle named Genjii via unknown means and started testing drugs on him. An eventual the buildup of side effects from the drugs granted Genjii the ability to fly. Reimu then exploited this ability and used him as a car on her searches for the remedy.
One day while searching she came upon a neglected and depressed Marisa who was angry that Reimu had been searching for the potion for such a long time and hadn't hung out with her in awhile. Reimu attacked Marisa, feeling it was necessary, and continued on her search. After once again failing to locate the potion Reimu returned to her shrine, only to find that a ghost, Mima, had taken up residence in it. Reimu had a battle with her and lost miserably (which was odd, considering the fact she beat an archangel and a master swordsman with only a stick and kickball). Reimu struck a deal with the phantom and allowed her to stay as long as she didn't wreck the place.
A month later Reimu was on one of her incessant searches when she came upon some magical ruins. At the ruin gates a crowd had gathered that consisted of Marisa, Mima and a bunch of other worthless people who never bothered to show their faces again after this event. Reimu fought her way into the ruin's center, which was then revealed to be a spaceship. The spaceship pilots congratulated Reimu on her skills and offered to take her to their perfect world. Reimu, however, did not listen and, thinking the pilots were hostile aliens, killed them, ruining interstellar peace world over.
Following the previous event, countless youkai began attacking the Hakurei Shrine for no obvious reason other than it was ruining the neighborhood's real estate value. Both Reimu and Marisa separately went to investigate in the mountains, because that's where everything is, the mountains. The girls murder an innocent youkai named Orange and eventually come upon a lake filled with blood with a mansion on an island in the center of it. Seeing as such a place would wholeheartedly welcome visitors, the two walked right in. The two were surprisingly attacked by many guards in the seemingly friendly abode, including a scythe-wielding demon appropriately named Elly. As the girls made their way to the center of the mansion they came upon a sleeping youkai named Yuka. Yuka was having a nice dream and was angry that she was awoken, in retaliation she decided to destroy the world with her awesome power of Master Spark. Luckily for the world Reimu stopped Yuka and Marisa stole her ability of Master Spark for her own. Reimu was a bit miffed that this placed didn't have the armpit remedy either.
Later Gensokyo is beset by more demons, this time from the demon world of Makai that Reimu entered when first searching for the remedy. Reimu is annoyed by the demons and travels to Makai via (where else?) the mountains. Once inside she finds Makai in a chaotic state and eventually makes her way to the dark castle of Pandemonium. Here she meets Shinki, the Goddess and creator of the once-peaceful Makai. She reveals to Reimu that when Reimu previously came down to Makai and defeated the archangel Sariel, the kind and loving ruler of Makai, she created an unimaginable amount of chaos that eventually leaked out and attacked Gensokyo, meaning that Reimu had caused the sufferings of hundreds of thousands of demons and youkai. Reimu makes sure that Shinki can never reveal this to anyone else by killing her and burning down Makai to stop the demons. Reimu returns to the surface as a hero for stopping the demons and is finally accepted by the people of Gensokyo for who she is. (Or at least who she pretends to be...) One cold day in winter when Reimu was feeling particularly hungry she took Genjii and made him into soup. She covered this incident up by claiming that a wizard did it.
Reimu continued searching for the Anti-Armpit Hair Remedy until the following summer, during which time she hung out with Marisa and apologized for maiming her earlier. It was at this time that a strange, scarlet mist started to cover the land. This bothered the residents of Gensokyo, but instead of accidently doing anything about the mist they just sat there and complained about it. Eventually the mist became so thick that it actually blocked out the sun, causing crop failures and famines. Unfortunately for the crops however, nobody seemed to care and many people just stayed silent and starved, hurting the farming industry and crippling the economy.
One day Reimu was searching when she was impeded by the fog which stunted her vision. Growing angry at the fog, Reimu attempted to kill it, as to her this is the basic response to anything. After attacking the mist to no avail she decided to head back to the Shrine, get Marisa, and head out to find and destroy the source of the fog. Reimu recruited Marisa and that night they set off to find the source of the fog, because they wanted to impede their vision even more. Unsurprisingly, Marisa and Reimu got separated in the dark fog and lost their ways, Reimu went on a forested route while Marisa ended up on a path to a lake.
As Reimu continued on into the forest it became increasingly dark and spooky. While wandering aimlessly Reimu came upon a Youkai of Darkness named Rumia. Convinced that Rumia caused her to lose her way, Reimu verbally attacked her, enraging Rumia. They fought, Reimu using danmaku, a newly discovered form of Bullet Hell used in overly complicated shooters, and Rumia using her darkness. Rumia attempted to blend in by covering herself in a shield of magic darkness, but unfortunately for her, not only could Reimu not see through the darkness, but she herself could not see through it, making her powers essentially worthless. Nevertheless, Rumia attempted to fight from within the darkness, but ended up crashing headfirst into a tree and knocking herself out, rendering Reimu the winner. Later Reimu found her way out of the forest.