Bishoujo Mangekyou -Tsumi to Batsu no Shoujo-

Yuuma was forced to take a hiatus from school due to unspecified circumstances that left him hospitalized. After a year apart, he finally reunites with Yuuri, his breathtakingly beautiful twin sister, and they start living together. Nonetheless, Yuuma harbors a secret that he can never share with her - he's head over heels for his own sister... As the truth inevitably comes to light, the love becomes an obsession that threatens to swallow him whole... [Translated and edited from the official site]