Binetsu Kuukan by Aoki Ume — Ongoing

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Akasegawa Naoya's mother remarried recently and he suddenly finds himself trying to get along with his new big sister Amane, a student of the prestigious Kasugano Girls' School. But his new big sister isn't like what you might first expect.

Chapter 1 released Jul 18 '14
Chapter 2 released Jul 18 '14
Chapter 3 released Dec 13 '14 Aaaaaangst Yuri crush
Chapter 4 released Mar 8 '15
Chapter 5 released Jul 26 '15