When I woke up Millie had already gotten up and was no longer in the room with me. I also got up and as I left the room I noticed that my friend's pillow was torn, which made me worried that something bad had happened to her overnight, maybe something to do with the changes that were happening to her.
I found Millie sitting on the couch in the living room, she had her back to me but I could see enough of her to know what else had changed about her during the night. Now she had a pair of horns that protruded from the sides of her head and followed her skull until they almost met and deviated, going straight up.
Millie was moaning while playing with her breasts, and approaching her I saw that she had stuck her tail in her pussy and was using it to fuck herself. She noticed my presence and said "Good morning Emma. I'm almost done here and I'll help you with breakfast." and began to moan, increasing the rhythm of her tail movement and stopping when she reached orgasm.
As she came Millie looked at me, she was still beautiful as usual but her black eyes, which had changed again and now had visible blood red irises, combined with the horns on her head made her a little scary.
"Now I feel better, I was very horny and couldn't concentrate properly. Why are you looking at me like that? Oh, it's because of my horns isn't it? They had already grown when I woke up, one of them pierced my pillow and got inside it when it grew, and I couldn't take it off without tearing it even more.
"Millie, this is getting worse. You need help right away before it gets worse." I said
"Maybe you're right, my horns can scare people. But look at their size and their positions, if I have any surgery to remove them I'm going to be left with two huge scars and huge holes in my hair. So I think it's best to leave it at that." Millie said
"I know, but you still need to get help. What if the changes happening to you aren't over and you become some kind of monster, or an animal that can't even recognize me?" I said
"You can stay calm, I won't forget anything. Now let's prepare breakfast." Millie said
"I'm sorry, but I can't ignore it. I'll make an appointment with a doctor for you right now." I said and took my cell phone, dialed the number of a trusted doctor and waited for him to answer
"I said I'm not going to any doctor." Millie said making a gesture of denial with her hands. When she did, before my call was answered, my cell phone flew out of my hand as if someone had forcibly snatched it from me and crashed hard against the wall across the room, falling to pieces on the floor in then.
I and Millie were scared with what happened and we just stood without understanding, then we prepare the breakfast without saying anything to one another, so we did not know what to say at that moment, as we did not understand the situation. It wasn't until we finished eating that we started talking again.
"I'm sorry about before, I didn't mean to do that." Millie said suddenly
"For what?" I asked
"Your cell phone, I didn't want to destroy it." Millie said
"You weren't the one who broke my cell phone, you didn't even get to it at that time." I said
"But I felt something strange in me at that time, as if some kind of energy left my body heading towards you, and then your cell phone flew away. It seems I'm not just changing physically, apparently I've acquired some kind of power." Millie said
"Even so, we can't be s...." I was saying but Millie held up a hand holding a napkin, then dropped it and took her hand away. The napkin was floating in the air for about 5 seconds before it finally landed on the table.
"Did you see? I tried to repeat what I felt in that moment carefully while making breakfast and realized I can do it. I still don't have full control, so I can only move light objects a little and for a few seconds.
"It proves that I've developed some power, but I don't know the full extent of my abilities now, or if new abilities might emerge if I keep transforming." Millie said
"If so then you must learn to control it better. What you did to my cell phone was an impulse you had no control over, we don't want it to happen again, next time it might be worse." I said and Millie agreed.
I changed and Millie got dressed, me having to help her into a shirt after she'd pinned and ripped another one on her horns, and we went down to the basement where she practiced mastering the use of her newfound power. On this day we were grateful to be on vacation and I helped her as much as I could. I helped her all morning, we took a lunch break, and went back to practice.
It was already starting to get dark when she fully mastered the ability to move things with her mind, being able to be heavy things and now having no time limit anymore. As we walked up the stairs from the basement Millie said she was feeling something strange on her back and asked me to look at her for what it was, I saw that there were two things stretching her shirt from behind and when lifting the shirt I came across a pair of wings that looked like a bat's, both of which were the same shade of purple as her tail.
Seeing that Millie's wings were getting bigger I realized what she was becoming and said "Millie, you're growing wings, and linking the kind of wings, your tail, your horns and eyes, I think I know what's going on with you. You are turning into a demon."
Millie looked at herself in the mirror after what I said and agreed, then commented "Makes sense, maybe that explains my new powers. But why did I start to transform so suddenly?"
"I have no idea, but if your transformation isn't complete then your new powers will also grow." I said
"You're not scared of me now that you know what I'm becoming, are you?" Millie asked
"I'm not afraid of you, because I've known you for a long time. What I fear is that if you stop being human you will no longer be able to live in our society, maybe I won't even be able to see you again." I said
"Well, let's see how things evolve. But don't worry, even if I can't live in human society anymore I'll make sure to see you from time to time." Millie said
I was relieved by this and we ordered something to eat. When Millie's wings stopped growing they could reach 4 feet in length each when fully extended.
Later we lay down to sleep, but as her pillow had been destroyed, she lay with me on my bed. With the size of Millie's wings we couldn't properly cover her with the blanket, so she wraps her wings around us.
I was having trouble sleeping due to the situation, but it seemed like Millie couldn't sleep for another reason, as she slipped her tail between her legs and started rubbing the tip of my vagina.
"I'm sorry, I'm horny. I also noticed that you're not getting any sleep, so how about if we fuck so we can rest better."Millie said
"I... All right, let's go." I said
Millie then got up and positioned me face up, then she passed her legs over me, she positioned her tail between her legs, keeping her firm in order to simulate a cock, and so she penetrated my pussy. It wasn't the first time Millie had fucked me, as we'd used strap-ons before, so she wasn't clumsy while fucking me. Just like when we had sex in the bathroom yesterday she underwent a new change this time too, Her entire body grew to make her much larger than I was, and her breasts grew larger in proportion to their original size than the rest of her body. We ignored her change and continued to fuck until we were completely satisfied, which for me only happened after I came 3 times.
When we were finally satisfied we realized that now there was a new problem, as with my friend growing up we both couldn't fit in my bed together. Millie stood up so we saw that she was now 7 feet tall, her breasts had grown to the point of being approximately J-cup at the very least. She watched for a while then asked me to get out of bed as she had an idea for the two of us to fit in there together.
I did as she asked, so she lay down on my bed and said I was supposed to lie on top of her, and so I did. My housemate closed her wings around me and I quickly fell asleep.