It was her instinct for self-preservation that had brought Soi Fon to the monastery. After that first devastating reunion with Yoruichi, she had realized that everything she had believed in had failed her. Strength, duty, honor, love, revenge - they had all crumbled to dust the day she had looked, begging and weeping, into Yoruichi's eyes, only to find pity and regret. They were all that she had known; all that her world in Soul Society could contain. So she had left, exploiting the chaos of Aizen's betrayal and her skills as the commander-in-chief of the Onmitsukidō to fake an untimely demise. She had then fled into the mortal world, looking for an elusive, fleeting thing for which she had no name. And finally, years later, when she'd found it, the monks had smiled at her and given her its name. It was the most powerful thing she had ever known, the one thing with which she intended to reclaim her life.
It was called peace.
She had learned it at the feet of an old monk. While sweeping the courtyard, she had wrestled with her broom in the same way she had wrestled with her life, her love, her pain, her self-loathing and her hate. He had asked her to sit next to him in the sun, and that was how it had begun. It was like no other training she had ever undergone.
Remember little one, he had told her one day, people suffer because they want things to be other than they are. For a long time, she had not understood. She had not been raised to understand the concept of surrender.
And then one day, she did. With painful clarity, she saw the long endless train of her life: the interminable stretches of wanting and struggling, broken only by brief periods of tremulous joy that had only led, in turn, to more wanting and struggling. She had striven to be stronger, had labored for Yoruichi's love; and when she had believed that she had failed at both, she had ended up hating herself and Yoruichi. Suffering lies in wanting what is not or cannot be.
So Soi Fon had discovered acceptance...and the peace that came with it. She was not as strong as she wanted to be. The woman she loved possibly did not love her back. It was simply the way things were. And for the first time in her life, Soi Fon decided that the way things were was...okay. It had been a profoundly transforming realization.
So when she discovered, weeks after her epiphany, that she could control the shunkō effortlessly, run the flash step twice as fast, and mark her hōmonka in half the time, she had laughed at the irony. She had eventually found an explanation in one of the old monk's teachings. When you no longer carry the burden of suffering, all your strength can go to wielding your gifts.
It wasn't very long after that that they had let her go.
The year after she had left the monastery she had spent wandering. There was so little she had known about the mortal world - the world she had been duty-bound to protect. She dispatched Hollows when she could, when she was sure she could evade detection. But primarily she learned.
It happened almost by accident, the encounter that had eventually led her to rescue Yoruichi. For months she had noticed the steady increase in Hollow activity. Then one day, the dam had broken and countless battles had ensued. She knew better than to stay in the city during such times. The risk was higher that she would run into the Shinigami. So she had headed for the wilderness - and found traces of a familiar kidō. On an instinct, she had followed the trail of spirit energy, and had intervened, just in time, to save Yoruichi from the white-masked horde.
And while Yoruichi had slept, Soi Fon had bid a silent farewell to her wanderings. The last five years had been a happy respite - one she would have preferred to have gone on for longer. However, rescuing the older woman had been a sign. It was time for her to take her second step back toward the life she had left behind.