Nyotai-ka Shitara Shouta na Otouto ga Hatsujou Shisugite Yabai! ~Hitamuki ni Motomerare Makuru Doukyo Seikatsu ga Yosugite Kokoro made Onee-chan ni Nacchau!?~

Being desired so fervently and living together under one roof, even my heart turns Femmy!?

Brothers living under one roof... The elder looking after the younger.
But one day, some bathing powder turns Big Bro into Big Sis!
There begins their days of chaos... the ideal elder brother turns
into an alluring busty beauty, a sexual object from the heavens!
...and little brother resist the urge to 'play' any more...!?

[From DLsite English]