The Troubling Declaration of Sisterhood Episode 1

Fukazawa Yumi's tie is fixed by Ogasawara Sachiko, her idol and the school's star, setting off a chain of events which would throw the shy and ordinary girl into the world of the prestigious student council. After Yumi walks in on Sachiko arguing with the Yamayuri Council over the school play they will be performing, Sachiko suddenly asks Yumi to be her petite soeur in an attempt to force her way out of the lead role.