GS-027 - I gave my sister a toy as a joke, but watching her use it led to us crossing the line.

My sister has become incredibly alluring lately, and I couldn't help but tease her. As a birthday prank, I gave her a sex toy. Even though she acted disgusted, I caught her secretly trying it out. Watching her made me lose all control, and we ended up crossing the forbidden line into incest. It feels so good that the toy is no longer enough for her.