Ane Pani

Jin (female) and Konoe (male) are twins and are just starting their high school career. Jin has always been a trouble to her brother, since she's very tough and violent, and generally doesn't behave like a girl at all. Konoe is determined that their high school life is going to be different, and he's going to make sure she keeps acting cute and feminine. But it isn't easy for Jin to pretend to be something she's not…

(Source: Ichigo Ichie Scanlation)