[Ishino Kanon(石野鐘音)] Oneechan ga Oniichan (お姉ちゃん♀がお兄ちゃん♂)[2016-02-27]
From:
[Mediax(メディアックス)] Futanari Secross!! (ふたなり・セクロス！！) - Vol.01 [2016-02-27]
Code:
https://www.sendspace.com/file/mj506c
There is another similar story to this one but I can't remember the author atm.