"Molly my dear sister... Wait, sister?! Mom, what the fuck did you do to me?! Oh, Molly... I believe we have a problem." The body of Mia Johnson exclaimed.
Molly, mentally drained from casting the near impossible spell, could only sigh as she looked upon the situation. She was so close. So close to making her dream a reality. So close. But so very far.
"I believe there's a second personality inhabiting my body. Your body? This IS my body! Who even are you! I'm Molly's goddamn son! Son? Molly, I thought you only had two daughters. Enough of this bullshit, mom. Fix me right now! Molly, I know you want me here more than this fucking bozo currently along for the ride." The body of Mia Johnson continued to argue with itself.
Molly shook her head in exasperation.
"There's nothing I can do right now. I just performed one of the most powerful spells in my knowledge banks. I'm drained. I need to recharge."
"You mean I'm fucking stuck like this?!" screamed Miles in the voice of Mia.
"Which one of you said that?" Molly said.
"You really think I would be that angry at you, Molly? I know you'll do the right thing and eradicate this so called son of yours" Mia stated calmly, with undercurrents of contempt for her phantom nephew.
"Of course. But who knows how long I'll take to recover?"
"Mom!?!? WHAT THE FUCK!?!? You're just gonna murder me?! Well, not murder you, persay... she'll just make you part of a better whole. Oh, fuck you, whoever you are. I'll have you know that I'm Mia Johnson. Well, I'm Miles. Glad to fucking meet you."
Oh boy, Molly thought. This was gonna be quite the situation to deal with.
Option 1: Inside their shared brain, Mia tries to convince Miles that life would be better as Mia. During this conversation, Mia is using her growing magic to try and manipulate Miles.
Option 2: Miles soon realizes he has his own set of magical powers, and tries to use them to change himself back. However, he is unable to control the magic, and it has unintended consequences.