Mahoroba Komachi Haruhino-san

Chiaki is a highschool boy who transfers from Tokyo to Nara, the ancient capital of Japan. On the way to school, he meets a girl with the appearance of a deer. He soons learns that she's the school madonna, Haruhino-san, and for some reason, he seems to be the only one who doesn't see her in her human form.

(Source: Houbunsha, translated)