Yang might be OOC in this
I do NOT own RWBY
This will take place in a small AU where Yang still loses her arm but not because of Adam and Beacon never fell also Yang hasn't got her robot arm yet.
Y/N's POV
I have noticed Yang is getting more angry at guys hitting on her and girls flirting with me since we're both dating each other for a couple of months now. So now that Yang is pissed off, she'll most likely go off into Emerald Forest to kill some grimm to relieve some stress and anger. I would go with her to make sure she'll be safe but she told me that she will be able to take care of herself. I might as well clean some of our dorm while I wait for her return since Yang's relieving her anger and stress, Ruby is out with Weiss and Blake is out on a date with Sun for tonight. I managed to clean most of our room since I shared a room with team RWBY. It was almost 10:00 pm when I finally finished cleaning the place. I wondered when Yang would be on her way back to the dorm as I sat down on a nearby chair.
A hour earlier...
Yang's POV
I was heading my way to the Emerald Forest to kill some grimm to relieve my stress and anger since I was tired of men hitting on me when I'm obviously dating Y/N. It also made me even more pissed off at the random girls who flirt with my boyfriend. I wondered upon a clearing where I found a pack of Beowolves and some Ursa. I charged forward activating my semblance as I smashed one of the Beowolves heads to pieces. After killing the first grimm, the others noticed me and charged at me trying to kill me. I ran at them and started to kill them one after the other with a smirk on my face. It was about an hour later when I finished off the last of the grimm, after taking a break to catch my breath I made my way back to our dorm when I heard the sound of rustling leaves. I turned to look where the sound was coming from and it was coming from nearby bushes. I cautiously and slowly walked towards the bushes where the rustling came from and as I got closer a bestial werewolf like grimm came out and slashed at me with claws, it managed to scratch me on the stump of other arm but not before I socked in right in the face instantly killing. I looked at where it got me and it looked like it didn't to any major damage. Anyway, I walked back to the our dorm and I knocked at the door since we usually keep it locked.
Y/N's POV
I heard a knocking on the door, as I was resting. I went to unlock and open the door to see who it was knocking on it. I opened it and saw that it was Yang. "Oh Yang you're back." I said as I let her in, I noticed a few scratches on the stump of her arm. "How did you get those scratches?" I asked her curiously. "Oh, this I got after I killed some grimm some weird werewolf like grimm came out of the bushes. Before I killed it managed to scratch me." "Well, I'm gonna go take a shower. You might want to clean and wrap up those scratches so they don't get infected." After I was about to get my sleeping clothes to put on after I showered, Yang gave me a quick kiss and said "Okay Y/N." I entered the bathroom and started the shower up. As the shower warmed up, I took off my clothes and threw them in the nearby clothes basket. I got in the shower and I started to washed my hair and body I thought to myself "Is it me or did Yang's eyes seem more of a yellowish color rather than the normal lilac color.
About twenty minute later I got out of the shower, put my sleeping clothes on and I exited the bathroom where I saw that Yang was in her pajamas with the scratches on her stump wrapped up in bandages laying down in her bed. Before I joined her I turned off the light then as I joined her on the bed she got on top of me before straddling my hips. As she then locked her lips with mine, our tongues then danced as they battled for dominance. Eventually Yang won as her tongue searched my mouth. While we were making out, the full moon was at it's highest and brightest shining through our room window since we didn't have the curtains closed. The light of the moon shined down on Yang as she then was starting to get hot and bothered as she started grinding her vagina on my groin. She then pulled away from my mouth as air is a necessity and we both were panting, catching our breaths. Yang then started grunting as she was beginning to gain muscle and her body started to bulk up. Her pajama pants to tear as her ass, thighs and legs was gaining more muscle and increase in size. While her transformation was continuing, her blonde hair was getting longer and shaggier as her scleras of her eyes turned black and her iris turned into a brighter yellow. Her hands were also starting to get bigger and was also forming big, black claws. As her growth growth of her lower half continued, it stretched and tore up her pajama pants as she began growing a tail out of her tailbone, she was moaning and grunting in pleasure.
The final portion of growth and transformation started when her feet grew in size as the sound of bone popping and stretching could be her forming wolf like feet. About a few minute later, I brought my eyes to the sound of tearing as Yang tore her shirt open as her breasts grew in size as her torso also was growing in size. Twenty minutes later her body had stopped growing as she was now growing blonde fur all over her legs and body. Her already decent size breasts had stopped at a large L size. Yang's face was the last to experience growth and transform. Her face stretched and grew as it formed a muzzle. Her teeth were getting larger and also sharper as she grunted in pain as her teeth became large fangs. Finally, her ears were elongating as they were also growing the blonde fur on them too. As her transformation finished, I had grown a large tent in my pajamas and Yang could tell as she grew a smirk on her face as she starting grinding against my hard ten inch dick. She and I were moaning in pleasure at the sensation we were both feeling. Then all of sudden she grabbed my pants and yanked them off with her new found strength as I pulled off the remains of her torn clothes.
Yang then quickly tore off my shirt before tackling me and as fast she could lined my dick up with her pussy before inserting myself while letting a howl of pleasure. "Holy shit, Yang your vagina is really tight." I grunted out. She then started going up and down as she was panting and growling in pleasure. While she was doing this, I reached up and grasped her enormous breast as I sucked on one while pinching and the twirling the other nipple with my other hand. Yang growling in pleasure as collapsed on top of me, lost her lust and pleasure. "More! MORE! MORE!" she growled lost in her lust. I complied as I didn't want her ripping me to shreds with those claws of hers, thrusting as hard and fast as I could into her pussy while increasing my sucking on her breast while occasionally switching to the other nipple. Ten minutes later of intense and heated fucking I felt a pressure in my balls as I was about to release. I could also tell Yang was close as her pussy started to clamp down on my dick. All of sudden, I felt Yang's juices come down onto my dick like a waterfall causing her to moan and also causing me to groan and release inside of her like a flood. Her womb soon swelled up like a balloon about to burst. "S-S-So much...inside of...me." Yang moaned as her eyed rolled up almost inside of her head. After we caught our breath from the intense sex. Yang then licked my cheek with her long canine like tongue. Soon after she drifted off to sleep. I soon started to drift off to sleep but not before thinking "Hopefully this isn't permanent, if it is I'm going to need a LOT of water." I thought before falling asleep.