Her Smile
Many people liked smiles. That's not such an unusual thing to like, as smiles are generally quite pleasant. To some people, however, smiles were something to be used against your enemy, and nothing more. Sesshoumaru was one of those people. Smiles portrayed happiness, and if one found the source of someone's happiness then it wasn't so difficult to manipulate them.
The only exception was Rin. Her smiles gleamed, they shined, and that magnificence was only multiplied when she directed the expression towards him. Her smiles were precious, and most of them were given to him (which made him quite smug).
He rarely returned her smiles, for he was an all powerful yokai! Showing what made him happy would not only give away his weakness, but endanger Rin as well. He would not have that! Even though he remained impassive, even though he rarely returned those smiles (or basic conversations for that matter), the frequency of which she bestowed upon him these gifts never waned.
It was when she was around eighteen summers that that smile began to change. Well, how it made Sesshoumaru feel, anyway. Her chubby cheeks had all but disappeared. She filled out almost any kimono perfectly. Her hair fell in silky waves to her waist, and her lips were full and plump. Rin had become a women. Her smiles never changed, nor did their frequency, but suddenly Sesshoumaru felt an odd tightening in his chest whenever she looked in his direction.
And when she smiled, the world stopped, and he could swear his heart started beating faster. At first, he thought himself ill. When this became a constant occurrence, however, then he really started to worry. For he knew that Rin's smiles no longer made him happy... No, they made him fill with desire and pure joy. He no longer liked Rin's smiles-he loved them.