Kyonyuu JK Saiin Choukyou -Kimoani wa Imouto o Milk Nomi Ningyou ni-

The protagonist, Hikida Tooru, is a shut-in living in his family’s home in the city. His high school-aged sister despises him. One day, Tooru buys a Bible from a religious solicitor who happens to stop by. Unbeknownst to him, it contains an aphrodisiac spell. Naturally, he tries it on his hated sister. To his shock, she becomes completely obedient to his every command. And so begins the humiliating prologue of turning his sister into a cum-drinking doll… [Translated from dlsite]