I have the itch to write something that isn't based heavily on material I have written before; and I am still planning out the sub-arc's transfer into a story format. As such; I am going to do a one-shot backstory chapter that is new material.
Warning: There are scenes of strong violence in this section
15 years before the start of the story:
The spellcard system is not even a thought. Youkai and humans are constantly at conflict; the only safe haven for humans being the Human Village and the immediate surroundings; as well as the Hakurei Shrine itself; and it's holy grounds; tended by the Hakurei Maiden; Askura Hakurei; who had a child 3 years ago, whom she named Reimu.
When a youkai goes too far; the Maiden would step in; using the divine sealing powers she had to exterminate the youkai. However; this was a reactionary event. A youkai would have to cross the line into the unforgivable before Askura would act. The maiden was always fearful of provoking the youkai to greater hatred of humans, and thus, leaned more to the side of the youkai in the eyes of the humans.
One night; a magician in the Forest of Magic was preparing an incantation; however; something went wrong; and her life was consumed with the very summoning spell she was attempting to use. The familar she wanted to conjure to do her bidding instead became one with her, transforming the magician into a youkai-daemon hybrid, a Fiend.
Fiends were dreaded creatures; that only thought of bloodlust. The fell beast sensed the largest collection of lives to extinguish, and headed there.
Towards the Human Village.
The five-year old brunette was sleeping in her bed; her spanner by her side. Unlike most in Gensokyo; she had a keen interest in science. Her parents were unusual for humans; they wanted the conflict between humans and youkai to end. The child's father had the ability to create barriers; although far weaker than those the Hakurei Maiden could conjure; while her mother was a healer. Both would do what they could to avoid conflict between youkai and humans from leading to death.
The little girl woke up; as she heard a voice from the living room. It was her teacher; and one of the most respected members of the villiage; Keine.
"There is a youkai heading right for the village." she said. It is clear that it's intentions are hostile, but the strange thing is; it's even attacking other youkai in it's path. This one is a bloodthirsty beast, unlike anything we've seen in years."
"We'll find a way to stop it; without us stirring up more hatred. If we humans kill it; we'll probobly just make more youkai angry and liable to attack us." the girl's mother said.
"If we can hold it off until the Hakurei Maiden arrives; we should be OK. If it's attacking other youkai as well she's sure to come to stop it." the father added.
"Are you sure about this? From what the lookouts have been saying it sounds like this creature is something you won't be able to stop... I came here to tell you not to get involved." Keine said.
"We're not going to let others get hurt when we can prevent it!" the mother demanded. "Hideaki; are you with me?"
"Yes; Hikaru." the father said; before facing Keine. "Even if we cannot stop it; we can buy time. We can save lives."
The two parents of the girl left the house; and Keine looked frustrated; before she noticed the ajar bedroom door.
"Ah; Rika; I'm sorry; did we wake you up?" Keine asked; bending down to the girl.
"I heard noises... another youkai's coming isn't it?" Rika said.
"Yes dear." Keine remarked.
"Why can't we just get rid of the youkai and not have to be scared of them anymore?" Rika asked innocently.
"Because youkai are a part of this land; and they themselves are hiding in Gensokyo. Most people don't realize this; but youkai are scared. They are not all evil; although some are; the Hakurei Maiden takes care of them."
There were cries from outside, and Keine stood up.
"Go to bed Rika. I need to go outside and help as well."
Keine left the house; and Rika went back to her room. But the noise of spells being cast and combat was too loud.
Then Rika heard a scream.
She got up out of bed; and left her room. Her hand shaking; she opened the door and wandered outside to the back of her house; onto a hill; where she could see the edges of the village from.
Rika could see a dreadful beast; it looked like a human in shape; but clearly was not. It's right arm was like a sword; and it's left hand had huge talons. The creature wore black; torn robes; robes that magicians usually wore; and it had wings which looked like a crow's; but badly damaged. It's face was disfigured.
Rika's father put up a barrier to hold the creature back, as Rika's mother tended to some wounded humans.
Then the creature; for the briefest moment; looked right in Rika's eyes.
Rika ran down the hill; back towards her house; as the creature flew towards her. A child. Easy prey.
It almost reached Rika; when a barrier formed between the creature and her; which cracked; but the monster bounced off, into a position between Rika and the door of her house.
The five-year old was terrified, as the monster lashed out with it's right arm; the girl rolling out of the way.
Then; the beast started to flail around; as if attempting to reach something on it's back.
"Run; Rika! Run away!" Rika's father said; Rika getting a glimpse of him on the beast's back.
Rika turned and ran, only to turn around again when she heard a cry of pain.
The monster had impaled her father on it's blade.
Rika's mother was rushing towards the creature too now.
"Let go of him!" she cried.
The monster's eyes just burned with bloodlust; as with one swing of it's left hand; it tore into the body of Rika's mother; and the continuing swing beheaded her father.
Rika had nothing to say. She felt nothing but despair; and fell to her knees; as the beast headed for her.
There was a bright flash of white light; and a miko in red and white was between Rika and the beast. But Rika did not care. She did not care for the battle that took to the skies. She did not care about Keine rushing over to her. Death was something one learnt about when very young in Gensokyo; and Rika; even at five; knew her parents were dead.
She only felt a small bit of satisfaction; deep within her; when she saw the fiend turn to ash. However; when the Miko walked towards her; she felt hate.
"Why did you not come sooner?" she spat at the Miko. "Mother and Father..."
She began sobbing. The Miko said nothing at first; she just turned away.
"News reached me too late." she said simply, before she flew off; getting insults thrown at her from the other humans for the delay as well.
"She always takes the youkai's side! We have to suffer before she comes!" Rika sobbed into Keine's arms.
That night; a dark fire was burnt into Rika's heart. The very fire that her parents had been trying to avoid creating. The fires of vengeance. Rika began to hate youkai that night; and this hatred grew as time passed; into her desire to kill all youkai; and those who would side with them; such as the Hakurei. What was worse; seeing her parents be mutilated in front of her damaged her mind; cracks which would only worsen as she grew older.
Two months later; a Scientist entered Gensokyo; called Rikako. Rika took a shine to her; due to their common interests; and Rikako adopted the orphan; the two moving away from the Human Village. Keine and the other hmans saw no issue with this; as they knew Rikako was responsible and strong enough to survive outside the village; as well as protect Rika.
Five years later; however; Rika's desire for revenge was growing too much for Rikako to contain. She had attempted to dissuade Rika from revenge; but with her talent; nurtured by Rikako's knowledge; Rika behind her back built weapons; with the purpose to exterminate youkai.
Rikako found out, and attempted to put a stop to Rika's designs; and a conflict ensued. Rikako was forced to flee; Rika's weapons being too strong; but the chemicals spilled during the conflict from ruptured containers had a side-effect on Rika; stunting her growth.
Rika relocated her base to the mountain ranges of Gensokyo somewhere Rikako did not know; and; a few months later; attacked the Hakurei Shrine... the start of her quest for revenge. By this time; however what was greif for her parents had vanished. Her origional drive was all but forgotten. She recalled little about that fateful night; since she was the tender age of five.
Al that remained was a destructive desire for complete Genocide; as well as madness. She was blind to all else.
It would be eleven years after the attack on the Hakurei Shrine that Rika would become the very monster she sought to destroy; and begin to see things ever so slightly differently.
It would be eleven years after her attack on the Hakurei Shrine; until she met Rumia.
Author Notes: Eh; this may be very cliche but it's a backstory for Rika. Her parents got killed by youkai; and Reimu's mother was too late to stop it happening; so Rika attacked the Hakurei Shrine in SoEW for revenge. The sight of their deaths not only made her want vengeance; but at her age; drove her towards madness. The combination of madness; time and a desire for revenge made Rika what she is now.
But an important point is that before the spellcard system; conflict between humans and youkai would only escalate to more conflict. Most accepted this as the norm; but there were those who wanted it to change. These included Rika's Parents; Keine; and the Hakurei. This hate is being overcome now; by people such as Keine and Mystia; but there are still many youkai who hate humans.
Reimu is 18 at the start of this story; [In-canon she should be about 18 atm, given the timelines and ages given in PC-98. If you look at things like Hopeless Masqurade it's not hard to see Reimu could be ~18] and Rika is actually 20 [But appears 10 due to her growth being stunted; and she is 21 by the time she meets Rumia].
As for Reimu's mother; she would have died probobly a year; maybe two; after the attack which claimed Rika's parents; about halfway between HRtP and this bit of backstory.
Names for the three parents in this story were basically Japanese names taken at random.
Again; this is basically filler material and some bonus backstory until I get the Sub-Arc sorted out. Apologies for the likely lower quality of the work.