Oneechan Dorobou

For Yuiko, she has no "freedom" whatsoever. Every single day, she's always been ordered around by her childhood friend, Aya, and her little sister, Chika, and she can't help but to obey them. Though, one day, she receives a love letter from a classmate! For some reason...Aya seems very annoyed by this.

(Source: Intercross)