Grimoire ~Ingyaku no Madousho ni Oboreru Yuri Shimai~

One day Asami witnessed a moment of lesbian kissing between the target of her yearning affections, Miyuki, and her dorm mate and friend, Kyoko.

Shocked and jealous, Asami felt her chest would burst, when a strange "voice" inside her own head spoke to her.

"Shall I grant your heart's desire?"

Asami followed the voice to the library, and before she knew it a book was in her hand. And the voice said,

"Relinquish your mind."

And she opened the Grimoire, and wished.