My Older Sister is the Committee Chairmen.

Minoru is the class president of her school, and she has a problem – a new transfer student named Ryuuzaki, who is the son of a well-known (and very handsome) gangster and quite the handful himself.

(from mangaupdates)

[Note see amazon link there are 2 versions the second one is titled "shin" meaning new. Manga updates has both of them listed as one (3 and 5 volumes) but they should be separate. The covers here now match the Shin version. After this is resolved remove this note]