Satsuki's New Clothes
This snapshot takes place during the series – after the rescue and before the big fight. (I am, indeed, staying away from specifics. The time should be obvious by the end.)
Who would have suspected that I would have a sister who wears clothes so easily? She pondered as she dropped the sheet wrapped around her worn frame. Somewhere, lecherous 'ooh'ing and 'ahh'ing reached her ears, but she had neither the time nor the energy to be concerned with what others thought. She braced for a moment, staring at the innocent-looking uniform laid out before her, and searched her inner self for a final burst of fortitude.
It was a strange sensation, slipping into clothes that weren't Junketsu. The former was cold, no matter how warm her room was or how often she had it ironed. It was stiff and resistant, conforming only when she demanded, and only when she concentrated with her full strength. And it was always painful to wear.
This one, Senketsu, needed donning to deal with the imminent threat of that younger sister, and putting him on required a different state of mind than with Junketsu. He was sentient but silent, willing but motionless, and he was meant to be worn by someone else. Inwardly, she cringed as she grabbed him, pulling him on piece by piece. All of these clothes were made for her.
It was just as painful donning him as it was Junketsu, but she bore it silently. Kiryuuin Satsuki does not fold for mere pain. She had no time to waste moaning over such trivialities such as sensation of feeling. No time to wonder how she looked in the armor that is Senketsu.
"Senketsu," she spoke aloud, addressing the clothes for the first time. "I want to stop Matoi from destroying everything I hold dear. I cannot do it alone. Please follow my lead." The clothing warmed in response, and she assumed that meant his compliance.
With that, the time for rest was over, and she ran to the top deck of the boat, knowing that her plan was in place and that she would just have to hold Matoi long enough to give the Elite Four time. She knew she was no match for her younger sister, and she knew that she would have to go all out just to stay alive. Just to give her plan a fighting chance. She was afraid.
Fear is freedom. She reminded herself.
"Senketsu, lend me your strength."