Kaoruko is the older twin with a pessimistic nature and lacks self esteem and confidence. She's not outgoing at all and barely talks to people. During the double date, her sister stays at Doumeki's side while Kaoruko spends most of her time talking to Watanuki but keeps her sight on Doumeki. Despite Watanuki encourages her to have a positive attitude which allow her to have more confidence with herself, Sakurako does the contrary and causes her sister to go back to her original attitude. This is why she ends up being a customer in Yuuko's Shop. She has an infatuation (crush) on Shizuka Doumeki.

(Source: xxxHOLiC Wiki)