Seinaru Megumi

This 4-koma gag manga is about a group of high school students who were childhood friends. Sei used to go to a fancy girls' school, but now she's attending high school with her cousin, Hiyori. Sei and Hiyori don't exactly get along, but they both like Sei's 'nanny' Megumi, the man who raised her. Now they go to school with Hiyori's childhood friend, Mitsumasa, and enjoy high school life with their classmates.

(Source: MangaHelpers)