Sebastian didn't know that Ciel had an older sister, In fact Ciel never planned on telling him until you showed up one day, sick and soaked. Ciel rolled his eyes prepared to turn you away but Sebastian felt a pang, not of pity. But he just felt the need to protect you. So he brought you in and helped you, Ciel couldn't care less. After you got change Sebastian was towel drying your hair

The young Master doesn't seem too fond of you..