You look down at your new "self", Gorgeous you think to yourself. If you were going to mix anyone with Amelia, you much rather it be this babe than your comparatively bland sister.
You calmly walk back upstairs, all the strange feelings from earlier are gone. Being a woman now feels like second nature to you. That is perfect for you will soon be Amelia. You walk back into your sister's room where Amelia is tied up,
You finalize your ideal self by merging with Amelia. You mostly discard your personality and adopt hers with a few minor changes from your old self. You keep all of your memory but also take in hers. Finally you take on her name.
You walk over to the full length mirror in... You guess you can call it your bedroom, your former best friend no longer has use for such a girly room.
You walk over to the mirror and upon seeing your reflection you are overtaken by a feeling you know all too well. You're feeling aroused and getting wet.
Your body is perfect, while it was gorgeous before, the last merge only made it better. And you've made sure that non of your heterosexuality was carried over, your body is now the object of your attraction.
You lay down on the bed and start to indulge yourself.