It's about the challenges a normal person faces when having a sibling that is "perfect." Kyosuke Kosaka had always been looked down upon or ignored by his family because he could never live up to his naturally gifted younger sister, Kirino. Even she barely acknowledges his existence, until he discovers her dark secret. It becomes up to him to keep her safe from a world that would smother her, and parents that would disown her...all the while dealing with her tsundere attitude.
-thanks to Mirai for the description.
