Onna Tomodachi wa Tanomeba Igai to Yarasetekureru

Hisaya Minato, an ordinary high school boy, has a slightly unusual friend. She is Aoi Hazuki, the most beautiful girl in school. For some reason, the two hit it off, and since they happen to live in the same apartment building, they gradually became good friends who go to each other's houses all the time. One day, Minato asks Aoi to show her underwear on the spur of the moment. At first, Hazuki is reluctant, but then she begins to roll up her skirt...?

(Source: Comic Newtype, translated)