She had known there was something about Ryuko Matoi that gave her pause, ever since she turned up at the Academy brandishing the Scissor sword and demanding to know about her father's murder. It wasn't till the second day when Matoi appeared, wearing that Kamui, Senketsu that Satsuki realised that there was something truly different about this girl that set her apart from the other students, even her Elite Four.
That feat alone was enough for Satsuki Kiryuin to take notice of the transfer student. And as time went on and Matoi continued to oppose her, Satsuki found she was beginning to feel something towards the girl. Respect maybe, or perhaps even admiration, her pride however would never allow herself to admit such things.
Soon Ryuko Matoi had become a worthy adversary for her to test the Honnouji Academy student army and the Elite Four against. Satsuki could see that Matoi was getting stronger with every battle, that she and the Godrobe, Senketsu were getting closer to becoming one. After the battle in Osaka, Satsuki knew that Ryuko's control over her Godrobe had surpassed even her own ability to control Junketsu. It was then that she knew Ryuko would be the strongest ally to have against Ragyo Kiryuin, her Mother.
And the plan had worked. Until the original Life Fiber activated, and Ragyo reattached her severed head to her body, and had then proceeded to beat Satsuki without mercy. Leaving her beaten and defeated in a pile of rubble robbed of both her dignity and kamui.
Satsuki could only watch, helpless, when Ragyo confronted Ryuko, and ripped the girls still beating heart from her chest.
"And here I thought you were dead. Daughter of Mine."
In that instant time seemed to stop and all noise fell away until the only thing Satsuki could hear was the rapid beat of Ryuko's life fiber infused heart in Kiryuin Ragyo's firm grip.
Trying to process what Ragyo had just said, Satsuki knew that Ryuko was the only one strong enough to stop the monster that was her mother. No. Their Mother, the monster that had birthed them only for her own selfish experiments.
And so she stood on trembling legs, her body battered and broken but her spirit and resolve stronger than ever. She stood up and charged. The only one that could save the world was Ryuko, and to do that Satsuki was the one that had to save her first.
Her Sister.
Ryuko.
