Her smell
How disgusting the scent of humans was to Sesshoumaru. They reeked of sweat, grim, and the most pitiful of all-weakness. Rin's scent was different. It reminded him of the flowers she loved to pick, and the clean breeze that ruffled through her hair.
As Rin grew, from a small child to an awkward teenager to a young women, that scent grew as well. It was no longer just sweet, her unique scent had gradually become so enticing that it was hard not to jump her.
This confused him, how could this happen? Sesshoumaru had practically raised Rin, how could he even think of her as his mate? Then he realized that none of it mattered, because he loved her.
It was the hardest thing he'd ever done, admitting that to her. He usually was completely indifferent, so lifting that mask-even to Rin-was very difficult. Even for an extremely powerful yokai like him.
As difficult as it may have been, it was definitely the most gratifying thing that had happened again. For once, he didn't care how the rest of the yokai felt about him, and he truly understood his father.