Akuma na Kuchibiru

Hana Yamada, a high school girl, gets sick after drinking alcohol during a mixer, and is rescued by a very cool guy who she thinks is a student. However, when he suddenly asks her if she's a elementary school student, Hana becomes very angry and kicks him, before running away. The next day, when Hana goes to the nurse's office, she finds none other than the very boy who'd made her angry, Shuuji Kidou...
(Source: Midnight Scans)