AN: We'll start with something simple: For Sakuya's origin, I'm simply going to take the common theory of Sakuya being a former vampire hunter and expand on it.
Sakuya Izayoi – from Huntress to Servant
[London, 15th December 1735]
It was a cold night and the snow gently floated down to cover the almost empty streets of London, coating every surface with a glistening white layer of tiny snowflakes. A lone woman walked the streets, a black cloak wrapped around her body, sheltering her body from the cold. Her silver eyes scanned the snow-covered streets until she spotted an old mansion. The building's garden was overgrown with thorns and weeds and the once-sturdy metal gates now rusted and battered. The building itself had wooden planks covering the windows and its walls were covered in moss. It seemed to be abandoned, but the woman knew better. She approached the gates and tried to push them open, only to find that they would not budge; this was not a problem as she gently placed one of her gloved hands against the frozen metal. The palm of her hand began to glow blue, and in an instant a burst of energy was released from her hand and had blasted the gates off of their hinges and into the garden. She briefly looked around to confirm that nobody had seen this before stepping through the opening and heading straight for the mansion's doorways. As she drew closer, she lowered her hood, revealing beautiful silver hair, almost identical in colour to her rather unusual eyes. The wooden doors to the mansion were not only much sturdier than the gates, but were rather surprisingly unlocked. The woman simply pushed the doors open and quietly slipped inside before shutting them.
'As I thought, it isn't abandoned…' She thought to herself, noticing that the grand hallways of the mansion were lit with candles. 'It must be in here… the vampire…' She took a step forward, flinching at the sound of a creaking floorboard and pausing as a result, before carefully continuing. She reached to her waist before gripping the handle of something and immediately slid the object from its place on the belt holding it and examined it: In her hand was a throwing knife that was beautifully crafted from silver; it was the perfect weapon for dealing with vampires and one out of the total of six, except she had a few special talents to ensure that she had more than enough knives needed for the job. Still gripping the weapon between her forefinger and thumb, she carried on once more until she reached a door, and heard voices coming from the room on the other side.
"My dear sister," came a voice, that of a seemingly young girl, "You don't need to worry about that. Yes, it is getting dangerous here, even for us, but we will be gone long before somebody comes looking for us. Let us just wait until Christmas, and then we will vanish into the night before the new year."
"Are you sure?" A second voice asked, that of an even younger girl, "I'm scared, big sister, I don't want them to find us."
"I'm sure, Flan," the older of the two spoke again, "The humans won't find us, I'll keep you safe."
The silver-haired woman heard their footsteps, but she was surprised as she had not expected a second vampire to be here. Shaking the thoughts from her mind as the door began to open, time seemed to stop. In fact, it had stopped, everything except the woman and anything she interacted with was frozen in place, and she immediately backed away, hiding in another nearby room and listening at the door. Time resumed, and she heard footsteps but nothing more. She carefully and quietly opened the door before peering around to look at the two.
The closest had short blonde hair and wore a long-sleeved black dress. More noticeable than that, however, were the girl's wings; each looked like a branch, yet they were made of a strange metal that was black in colour. They also had a total of eight coloured crystals hanging from each wing in the same pattern. The two crystals closest to the base of her wings were cyan in colour, and then the next along was dark blue, then violet, then pink, then orange, then yellow, then lime green, and then finally cyan again. There was a red ribbon in her hair, but nothing else could be seen from behind. In front of her was a slightly taller girl with grey leathery bat wings. She wore a pale pink dress with a matching mob cap that had a red ribbon tied around it. She paused and spun around so quickly that the woman didn't have time to hide. Her face was fairly rounded and she had scarlet eyes, which were currently glaring at the woman.
"Flandre, get behind me, now." She told the younger vampire, a spear made of red energy forming in her hands."
"Remi? What's-" Flandre began, only to freeze at the sight of the woman as she turned around. Like her sister, she had scarlet eyes. Her mouth was open in shock, revealing a total of four small fangs – two on each jaw – and erasing any doubt in the woman's mind that she was indeed facing vampires. In an instant, time paused again and the woman threw the knife. While only one knife was thrown, time continued and the two vampires were faced with five of them. The older of the two, who had been referred to as 'Remi', immediately darted in front of her sister and blocked the knives with her spear.
She spun around upon realising that the woman was gone, until Flandre created several glowing red orbs and fired them behind the pair, revealing the woman's new location even though the attack missed.
"Ah, there you are," Remi said, frowning and glaring at the woman, "Now then, can we show a bit of formality and introduce ourselves? I am Lady Remilia Scarlet, head of the Scarlet family of vampires and a descendent of Vladimir Tepes himself. I suggest you remember that, if I let you live. This here is my sister, Flandre. As you're about to find out, I don't take kindly to her endangerment. Since you burst in here uninvited, perhaps I could at least have a name?"
"Kaika no Yoru, and I am the last thing you monsters will ever see!" The woman announced, her voice filled with confidence as she tossed her cloak to the floor to reveal a leather cuirass and grey trousers and a matching top underneath the cuirass, allowing for mobility, as well as the belt holding her knives.
"Wonderful…" Remilia sighed. "I would assume that you're foreign, judging from your accent and name, and you're not the first vampire hunting fanatic to show up on my-" Then she took in everything that this woman had said. "-Excuse me, monsters? You waltz into my home, attack my sister, and yet we are the monsters? How insulting, first you assault my sister and then label us monsters? I'm afraid that this little squabble just took a personal level, and you are not going to like that." In an instant, several red chains of energy tipped with sharp points formed behind Remilia and lunged towards Kaika, some to restrain her while others appeared to be aiming to impale her. Of course, she once again froze time and ran forwards so that the chains would miss before throwing another knife, except it seemed to split into a total of nine mid-flight and they froze while moving towards Remilia. Time once again began to flow and Remilia was caught off guard, taking a knife straight through her chest while several more stabbed into her arms. She staggered back before looking back at Kaika, a fierce look of determination in her eyes as she pulled the knives from her own flesh and simply dropped them to the floor, her injuries healing in mere seconds without a single scar.
"They may be silver, but you'll have to do a little better than that." Remilia smirked, tossing the spear in her hand while more red chains formed around Kaika to restrict her movement. This was quickly followed with two bright blue orbs which quickly fired beams of energy at Kaika. Were it not for her powers, death would have been all but certain for her. As such, she was thankful when she not only froze time, but was able to manipulate the space around her and widen it to provide enough space to dodge the attacks. When she allowed time to resume, she was able to avoid taking even a scratch, much to the Scarlet Sisters' surprise. Remilia thought to herself for a moment before causing the chains to wrap around Kaika's wrists. She then calmly approached the surprised and struggling vampire hunter, moving the chains to allow her to get closer.
"Now then, you've a lot to make up to me after that performance," Remilia told her, "I was holding back, but now I'll give you a choice."
"What could you possibly offer me?" The woman asked, still struggling to get free.
"Your life, in return for your service. You did endanger my sister after all." Remilia shrugged. "Failing that, fighting always makes me feel a little peckish, but it would be a shame to see such a pretty face go so quickly."
"Why would I serve you?" Kaika snapped, struggling even more than before.
"Because I'm sparing you," the vampire's reply came quickly, "Despite your offences against the Scarlet House, I'm willing to forgive you on the terms that you serve me. Maybe then you'll see that not all vampires are bloodthirsty brutes."
Kaika paused, she stopped struggling and she seemed to be in deep thought for several minutes until she eventually nodded as Flandre approached them, clutching her sister's hand.
"I will serve you, miladies."
Remilia smiled, even if the sudden change surprised her. "Good, but I'm afraid that you'll need a new name since Kaika no Yoru brings bad memories. How about… Sakuya Izayoi? Yes, that sounds perfect." In an instant, Kaika, now named Sakuya, was released.
"Now then, Sakuya. You can rest for today while you get used to your new home, but tomorrow we will find you a new outfit more fitting for your role, and while we're at it get one for Flan, and then you can get to work fixing the damage you caused," Remilia replied, "You've displayed some interesting abilities, so I think you can handle that."
"As you wish, milady," Sakuya replied with a nod.
Now that she had been taught a lesson in humility, Sakuya would travel with the very creatures she once sought to exterminate as both a maid, and her mistress' last line of defence. They would eventually settle in Gensokyo, and there they would stay. While Remilia would be hard on her new servant at first, she would eventually come to truly forgive Sakuya, and the two would share a bond of unwavering trust in each other.
