Her Eyes
He supposed that those big brown eyes were what made him bring her back from the dead in the first place. When he first met her, Rin stared at him, eyes wide. He supposed that she had found him fascinating. Brown eyes weren't that fascinating, at least not to the demon Sesshoumaru. But Rin's, even as a child, sparkled with intelligence.
A part of her eyes that he didn't adore, would be the depth to them. The depth that spoke volumes about the pain and suffering that she had become accustomed to in her youth. In a way, he loathed this part of them. Not only had her pain come to pain him, but these scars reminded him of how he had left her so long in that forest, in that village.
He had been such a fool then, thinking to himself what a sad excuse for a human the dirty and bruised young girl was. Now of course, he realized that she was simply showing him her kindness. That of which he was undeserving.
But those scars that could been seen in her eyes, the ones that were only visible to those who looked for them, lessened over the years she spent roaming the countryside with him and Jaken.
One day he came back from one of his battles with a lesser demon over a territory dispute. He came back to the spot he had left her and the pesky toad, and she smiled up at him, eyes sparkling. He had realized with a start that those scars had disappeared.
Oh yes, the yokai just loved Rin's eyes. They reminded him of the earth beneath his feet, and they gleamed mischievously most of the time. Most of all, he loved those eyes because they spoke of how with each passing day he returned to her and she waited for him, they healed each other's scars.