Your friend is a fan of vocaloids so he wishes girls vocaloids to be real and be here in a cute form.
When the wish is fulfilled, you feel different, with more air coming to you, when you hear a cry of joy, from a girl:
Ahh, Miku and Luka are here in my room, that's great, with pretty ears and cat's tail, although in house clothes, they still look great; you see that the girl who speaks is Rin Kagamine.
From what she speaks you see by your side and there is Miku, you see yourself, confirming your fear, long pink hair, big breasts, thin waist, wide hips, softer, feminine body, you touch your head feeling cat ears, you feel a tail coming out from behind your body, you wear a short black nightdress, you feel afraid to see your crotch, but you feel that you have female organs there.
The Miku girl, react the same, the Rin girl asks them why that way of acting, then you take her to look in the mirror, she looks surprised and then she starts being happier yet, you decide to tell her who you are, they tell you their names the same and you confirm that Miku is your roommate and Rin is the birthday boy.
She feels a little bad, now that she knows what happened to you, you are told her not to worry, you are still fanatics of these, although not too much like him, and as it is her birthday they accept to spend some fun together, until they are tired