Kare wa, Imouto no Koibito.

Miyuki is a timid florist, frustrated with her non-existent love life. While down on her luck she runs into an old classmate (and crush) of her's on the street. Things are going great when her younger sister, Haruka, who has taken away every guy that she's ever liked, begins to weasel her way between them. Can Miyuki overcome her obstacles and fight for the man she's loved since high school?