Nekomonogatari: Kuro

Synopsis

It's the beginning of Golden Week, before the events of Bakemonogatari. After Tsukihi kicks Koyomi out of bed, he takes the opportunity to ask her about his growing feelings for a new classmate of his, wondering if he has fallen in love with her. Tsukihi deduces he is merely sexually frustrated and suggests he buy some porn magazines to relieve himself. After a brief meeting with Karen, Koyomi leaves home on his bike, on the way encountering Tsubasa Hanekawa, his classmate, sporting a large bandage on her left cheek. Tsubasa confesses to him that she was hit in the face by her foster father and asks Koyomi to not tell anyone about it, offering to grant any request in exchange for his silence; however, Koyomi only asks her to let him use his blood to heal her wound.

(Source: Wikipedia)