You use calm/pacify magic which works on any person or animal/monster and you also have healing magic which you'll see why later on in the story.

And as usual Mirajane might be OOC in this.

Y/N POV

I was sitting down at the bar of the guild chatting with Mirajane who was a good friend of mine, while Natsu and the others were fighting it out not far from where I'm sitting as usual. "So Y/N, how well did your last quest go?" Mira asked me while I was watching the fight. "It was pretty good. The villagers just wanted me to calm down some of the nearby monsters so they won't attack the village." I replied. While we continued to chat with each other our conversation was interrupted as Erza went to break up the fight because Natsu's and Gray's fighting made her strawberry cake fall on the ground. "Uh-oh, they're in for it now." I said feeling Erza's anger radiate from here. After the fight was broken up Mirajane and I continued our conversation. "So Mira, want to join me on a quest when you're done here?" "Sure, just let me finish up with these cups then we can go." she cheerily said. Soon after she finished the dishes, she and I made our way to the quest board. "Hm, what to choose...Oh, this seems easy enough." I said grabbing one of the quests before showing Mira. "All we have to do is clear a cave of monsters so they don't attack the village that the cave is close to." "Seems simple enough." Mira said while looking at the reward. "Weird, the reward is pretty high for such a simple quest." "Yeah, you're right but hey we can do this together. You got your demon morph magic and with my healing and pacify magic we'll be fine." I said as I gave her a calming smile. "Anyway, let's go get this crystal."

We soon left the guild and made our way to the village where the village elder was waiting for us. After telling him we were here for the quest the elder told us that the cave was nearby and he wanted us to clear it just in case any of the monsters get the idea of leaving the cave and destroying the village. He then pointed us in the direction of the cave we needed to clear. We soon started to make our way to the cave and on the way there, a question popped up in my head that got me curious. "So Mira, what kind of monster do you think will be in the cave?" "Hm, I don't know." About ten minutes later, we made it to the location where the cave is. We then entered the cave and after ten more minutes of walking through the cave we entered a large chamber of the cave with almost twenty different monsters around. The monsters soon noticed us and then charged at us. I may not have any offense type magic but I could still hold my own in a fight. Mirajane used her Take Over magic to shift into her satan soul form and charged at the incoming monsters with me close behind her with my healing magic. It was almost an hour when there was one monster left. I received some damage while Mira had almost to no damage done to her. 'Damn, she's strong as hell.' I thought to myself. After healing Mira and myself we wandered around the cave for a little bit to see if every monster was dead.

As we were walking around a corridor of the cave we came across and old wooden door that was locked. "Hey Mira, you want to bust open this door?" "Sure." she replied back to me before breaking open the door with her strength. As we entered the medium sized room to check to see if any more monster were hiding, I saw a pedestal holding up a strange purple glowing crystal with dark energy sparking out of it. "What is that?" I shook Mira's shoulder making her look at to where I was pointing. "I don't know." Mirajane said while shifting back to her normal self while we walked closer to inspect the crystal. Mira then went to grab the crystal to inspect it but before she grabbed it, I grabbed her shoulder from stopping her from getting any closer. "I don't think that's a very good idea Mira." "Don't worry, I'll be fine." she said before brushing my hand off her shoulder before grabbing the purple crystal and inspecting it. "See I'm fine, nothing bad happened to m-" before she finished her sentence the crystal shocked Mirajane causing her to fall back wards and dropping the crystal causing it to shatter upon impact on the ground. "MIRA!" I exclaimed as I ran and caught her. " Are you alright?" I said to her in worry. "Y-yeah, just some pain from the energy shocking me. "I told you not to touch the crystal." I then sighed. "Come on, let's get out of here and turn this quest in so we can get our reward." I said to Mira.

As we made our way into the large section of the cave where we fought the monsters, Mira suddenly stopped in her tracks while clutching her sides in pain while grunting. "Mira, what's wrong?!" I said to her as I quickly ran to her side. "My body, it hurts...so...much!" she said as she groaned in pain. All of sudden her legs started started to grow and gain muscle as they had started to tear her dress. Her feet were also growing as they broke through her shoes. All I could do was just back away and stare at her in shock as my best friend started to get taller as her legs were getting thicker and longer, not stopping until she was twice my height. "Y-Y/N, help me please?!" she pleaded with me as her growth moved to her arms. Her arms soon started to grow and gain muscle until her muscles were the size of basketballs. Her nails then elongated a little bit until they were an inch long. The growth then moved to her torso as it began once again causing her body to bulk up. Mira was groaning from the experience of her body gaining more muscle as she she soon developed a noticeable eight pack. Her breasts were the next to grow as they strained against her dress and bra as they grew into the size of large beach balls. As her already decent sized breasts were inflating even bigger which caused her to moan in pleasure. The last part of her to change was her ocean blue eyes to switch to a bright red and making her change to her Satan Soul form

After her growth had finished she towered over me as she was twice my height and I was six feet tall. Her dress was gone at the top exposing her bra while the remains of the dress were around her waist hiding her panties from view. All of sudden, Mira had a look of rage on her face as she then brought her fist down at me causing me to widen my eyes in shock as I quickly dodged to the side. I looked at where I was standing was a large crater. "Mira! What the hell are you doing?!" I yelled at her in shock. "Kill, kill, kill!" she roared as she ran at me. "Shit, the crystal must have caused her to lose control of her Take Over magic after shocking her." after I finished that sentence she rushed at me with great speed causing me snap out my thoughts and duck as her punch my a large dent into the cave wall. 'Crap, I need to use my pacify magic to calm her down if I don't I toast." after I was a good distance away I began channeling my magic and as I aimed it at her, Mirajane ran at me. "Almost there." I said as I was almost finished channeling my magic. 'NOW!' I said as I released a F/C beam of magic at Mira. It it her directly but not before she hit me in the side breaking my left arm and cracking a couple of my ribs as I rag dolled into the wall of the cave making me cough out a bit of blood. "W-where am I?" Mira said as my magic snapped her out of her rage. "I see my magic...guh...brought you out of your rage." I said as I sighed in relief causing her to look where I was. "Oh no. Y/N!" she gasped in horror as she ran towards me. She then changed back into her normal self before lifting me up. "W-what happened to you? Who did this to y-you?" she asked me. "You did. After you got shocked by that crystal, you lost control of your magic and went into a rage and attacked me." She then started to sob as she held me close to her. "I-I'm so s-s-sorry." she choked out as she continued to cry. "There's no need to be sorry. It wasn't your fault." I told her as I rubbed her arm to calm her down. "Now, can you put me down so I can heal myself?" I asked Mirajane causing her set me down. I then used my not broken arm to use my healing magic to heal any internal damage that I had received. After a while of waiting my injury mostly healed causing me to stand up. "Thank god for my powerful healing magic. If I didn't have such powerful healing magic I would've been dead by now." "Now the only problem is how are we going to explain this to others."

Time Skip...

After turning in the quest and receiving our reward we made our way back. We first stopped at a clothes store so we could get some new clothes for Mira since her current clothes were ripped due to her growth. It was awkward for the both of us because of the people staring at us mostly at Mirajane due to her new size. Luckily we found clothes that would fit her and after making our purchase we made our way to her place to drop off her new clothes and so she could change into something different. I waited outside her house while she was changing and after a few minutes she came out in a blue dress that matched her once blue eyes since they stayed red after her rage was gone. When we entered the guild it was silent since everyone was shocked at the sight of Mirajane's new body and size. They asked me what happened to Mira and I told them what went down. After that they all went back to there usual schedule. I sighed as Mira went back to work as I sat at the bar where I usually hang out at. A while later Mira asked me if I'm still fine after taking that punch from her when she went berserk. "Yes, I'm fine Mira. You don't have worry about me." I told her while giving her a reassuring smile. She blushed as she saw my smile and continued to work by serving alcohol to the other's and cleaning the dishes.

Some time later, night time had fall as I helped Mira finish up cleaning up the tables and dishes in the guild. After following her outside she then locked up the guild and made our way to our houses. Before we split up Mira grabbed my shoulder stopping me. As I looked up at her, I noticed that a blush was growing on her face. "Um, Y/N, I've been wanting to ask you something lately." "Yeah, what did you want to ask me?" I question her. "I was wondering if you wanted to be my b-boyfriend?" she stuttered as her blush grew even brighter. "Yes, I would love to be your boyfriend." I answered her as she gasped in happiness before picking me up and kissing me. Feeling her kiss me made me happy as I knew that my crushed had a crush on me. We then broke apart as we took some breathed in some air. "So want to take this to my place?" I asked her as I smiled at her. "Yes, I would love that." she said as she carried me in her strong arms. We then arrived at my house as she set me down and I then unlocked the door so we could began the fun. I then shut the door and locked after Mira got in. After setting down the key on a nearby table we made our way to my bedroom and Mira took off her clothes as I took mine off leaving both of us nude. When she sat down on my bed, I was glad I didn't have a bed-frame since it would of broke due to her size and weight. "Let's skip the foreplay shall we?" she said as she spread open her legs revealing her pussy to me causing my dick to harden. I lined up my dick and slowly slid it in her as we both moaned in pleasure. Soon after I began thrusting in and out of her pussy making Mirajane moan in bliss. While I thrusting into her, Mira grabbed her large breasts and pushed them around and kneaded them like dough. The sight of doing this made me pick up my speed as I began to rapidly thrust inside of her vagina. About twenty minutes later I felt a building pressure in my dick as I was nearing my end. I could also tell Mira was close too due to her moans were getting louder and the pussy was getting tighter. "Mira, I'm g-going to..." "Inside me please!" she begged me. Not long after she had came on my dick making me also reach my climax causing the both of us to let out a loud moan. 'Thank god, I bought a house with sound-proof walls.' I thought to myself as we came off our respective highs. "We should do this again sometime, Y/N." she said as I climbed on top of her and rested on one of her almost bean bag sized breasts. "Yeah, we should do this again and that was great but for now let's some rest." I tiredly replied back. Soon after saying that we both fell asleep into the night as we both enjoyed each other's warmth.