(Diaz Household, Marco's bedroom)
Marco was getting ready to go to school, though the classes wouldn't begin until a half hour later, just as Star barged into the room. "Hi Star." Marco greeted with slight guilt. "Has your asshole recovered from...last time?"
"It's perfectly fine now, thanks for asking." Star replied. "And now that you mention it-"
"We're not going to go doggy style again just to see if the last one was a fluke."
"I don't mean that, I'd rather never go through that pain ever again." Star replied, cringing as she remembered what happened and then shrugged it off. "No, I found some more interesting things in the internet and I thought it would be good to try them out as the opposite gender."
"And why do we have to turn into the opposite gender?"
"Just because!"
Marco remained silent and put on a serious stare while crossing his arms, but he eventually gave in once she put on the puppy dog eyes. "Fine, Star, but again, this probably won't be very pleasant."
"I'm fully aware of it Marco, but my curiosity's got the better of me!"
With that said, Star waved her wand and yelled "Gender Transformation Energy Pillar!", which covered both teenagers in pillars that turned their genders into the opposite one. Once the pillars vanished and the transformation was complete, Star had shorter hair and Marco had really long hair and eyelashes.
"And now, to verify I did this right!" Star proclaimed in a deep voice.
The duo stripped themselves naked and went to look at their mirror. "Hey Marco, you look great with a feminine physique."
"Well, you don't look half-bad in that male body, Star." Marco uttered in a rather high-pitched voice.
"Yeah, I look fine. I wonder how the." Star remarked before she slowly put her dick into erection mode. After looking at it for a few seconds, she took out her wand and said, "I think I'll make it bigger."
Star started to increase her dick and her erection, but the bigger it got, the dizzier she felt. "Why am I feeling dizzy?"
"An erection requires blood, so the bigger the dick, the more blood that's needed to maintain the erection."
Having that knowledge at hand, Star undid the spell and her dick returned to normal. "Okay, so no erections for the moment."
Nodding in agreement, Star and Marco went for each other's clothes and put them on as Star explained her plan.
"Now, to specify what we'll do: Marco, you'll try to seduce someone, then try to use your sexual appeal, and then you'll fight against a tentacle monster. Meanwhile, I'll try to be flirty, flash my junk at people, and then I'll cum inside something! Am I clear?"
"Yes, and now I regret not asking that first before the gender change." Marco replied before reaching for his pockets and taking out the inter dimensional scissors, which gave him an idea. "Hey, do you mind if I use the scissors to do my stuff in another dimension?"
"Sure, go suit yourself!" Star answered with a wide smile. "Meanwhile, I'll go to the academy to do my stuff!"
With that said, Star gleefully left the room as Marco cut open a portal and jumped right through it.
(At Echo Creek Academy)
Star quickly went inside, ran across the hallways and went into Miss Skullnick's classroom, where in she went to Brittney. When the cheerleader noticed the male Star, she simply asked, "Why do you look like that?"
"Marco and I changed genders!" Star cheerfully replied.
"Huh, weird stuff as usual."
"By the way, wanna hear a joke about my new dick?" Star asked, earning a confused glare from Brittney in response. "Nevermind, it's too long."
"Hey, wanna hear a joke about my pussy?" Brittney replied, and she earned an excited nod from Star. "Nevermind, you'll never get it."
Star cringed and backed away as her classmates uttered "Oooh" in surprise. "Seriously, Moonian Princess, you were weird before, but now you're a freak for your little joke alone!"
The princess looked around and saw the students nodding and shrugging with sheepish smiles, which made Star put on the hoodie and leave the classroom.
(Meanwhile, with Marco)
Tom went into his room and saw Marco in female underwear on his bed with a suggestive pose. "Tom, do me like one of your French girls." He said in a sultry tone.
Some seconds later, Marco bolted out of the room holding her clothes while dodging an enraged Tom's fireballs. "AND DON'T COME BACK, SLUT!"
(Back with Star)
Star, still with her hoodie up, looked at Marco's locker in embarrassment. Then, once she saw Hope and some girls heading towards her, she smiled before remembering her other thing and pulling down her zipper. "Hey Star, why are you a different gender today?" Hope asked once she and the girls reached the temporary boy.
"Marco and I decided to change genders in order to do stuff that was inspired from the internet." Star hastily answered. "And speaking of the internet, take a look at this!"
Star turned around and revealed her dick to the girls, who flinched and backed away a little. "So, who wants a piece?"
The girls remained still with disgusted looks for a while before Hope kicked Star's balls, which stunned Star long enough for them to run away. Then, as she grabbed her balls, Ferguson and Alfonzo approached Star, gave her worried looks and helped her get up.
"Star, I think your balls need a rest." Alfonzo remarked.
(Back with Marco)
The temporary girl barged into Ludo's castle, where he was met with instant hostility from Ludo and his minions. "Who dares enter my castle without permission!" Ludo furiously questioned.
"The girl that will make your dreams come true." Marco said suggestively as she shook her hips at Ludo.
The kappa failed to be intrigued. "Are you trying to seduce me? Because it isn't working. I mean, you look like a teenager at best, that's a sure sign that seduction won't work."
Then Marco pulled his shirt down to let Ludo see his breast...which wasn't much to begin with. "Come on, Ludo, can't you let me stay?"
"Seriously, your seduction technique isn't working on me." Ludo replied as he pushed Marco away. "You also remind me of someone I hate."
Marco then went a little too far and leaned towards Ludo and grabbed his beak while giving him a seductive stare. "Please, Ludolicious with a cherry on top, let me stay."
Ludo put on an annoyed look before he personally kicked Marco out. "Seduce me once, shame on you, seduce me twice, shame on you too, seduce me three times...and this is what happens." Ludo stated as Marco got up and ran away. "Weird girl."
(Back with Star...again)
Star rested on a bed at the nurse's office while a bag of ice was covering her balls, reducing the pain as Alfonzo and Ferguson looked around. "Thanks for the ice, guys." Star said in relief. "I'll keep this experience in mind every time anybody gets hit in the groin."
"No problem "So, anything else you gotta do before you turn back into your original gender?"
"Yeah, penetrate something and cum inside it." Star answered.
While Alfonzo, Ferguson instead found a fully functional female mannequin's torso and showed it to Star, who was confused at the sight. "Why does the nurse's office have a mannequin that looks like a woman's torso?"
"They used to teach students how to do sex properly in the night classes." Ferguson explained. "Somehow, the only thing remaining from those classes are female mannequin torsos."
"I'm confused, but hey, after I do this I return to normal so let's get on with it!" Star replied confidently before Alfonzo went to her with a bag of condoms, which got her attention. "Ooh, what are those?"
"They're condoms." Alfonzo answered as he took one condom out and put it on Star's dick. "With these on, not a single sperm will end up in the mannequin itself."
Star smiled, grabbed the mannequin and, after feeling a little bit awkward about what was happening, started to penetrate it. To save you the details, Star did this for a few minutes before cumming, which left her exhausted once she finished.
Once she took out her dick and the condom, however, she immediately noticed she didn't even fill a third of the condom. "This is it?" Star complained. "I honestly expected to fill at least half the thing."
"Well, Star, you can't really expect much when you did this rather quickly." Alfonzo replied as Ferguson nodded in agreement. "And besides, you just need to accept reality isn't the same as fiction."
With that said, Star sighed sadly as she turned to the ground. "I guess you're right."
(Back with Marco...again)
A random tentacle monster was attacking a bunch of people when Marco arrived and hit him with a swift kick, which made the monster turn his attention to the confident girl. The two engaged in a short brawl where they were evenly matched up until the monster grabbed his leg and put him on the ground. Then, as Marco struggled to get up, the monster slowly went towards him.
"Okay, looks like I failed to beat you." Marco uttered before he closed his eyes and turned away. "Ravish me gently, tentacle monster."
"Whoa, hold it, hold on, what?!" The monster shouted as he backed away and helped Marco get up. "I'm an actor, girl! All that monster crap was just me trying to act like a convincing monster for a movie I'm starring in, because in one scene he gets attack by a girl! And besides, you're not even a legal adult yet."
"So you're not going to ravish me?"
"Why would I ever ravish you? Outside of the age factor, we're not even the same species!"
"I thought you were just a mindless monster who raped everything in sight."
"A mindless monster?! I may not look like it, but I have feelings just like everyone else in the multiverse!" The monster snarled before adding, "And you, milady, have hurt and offended those feelings with your words!"
With that said, the tentacle mass monster cried a pool of pink tears as Marco watched the monster run away before looking at the ground in regret.
(Back at Marco's bedroom, 15 minutes after the previous stuff)
A sad Star sat on Marco's bed as she remembered what had happened today and what she had learned. And then a portal opened and Marco jumped out of it, and he closed it before sitting next to Star.
"Hi Marco."
"Hi Star."
"Well, looks like we both found out that reality is very different from fiction." Star remarked. "I tried to be flirty and got humiliated instead, I flashed my erect dick and got kicked in the balls, and when I came inside a practice mannequin I felt practically drained afterwards."
"Yeah, those things tend to happen, and I didn't have it any better." Marco responded. "I tried to seduce a man and I was forced to retreat, which is understandable, but then I tried to win Ludo with my sexual appeal and he kicked me out of his castle, and then when it looked a mass of living tentacles was going to ravish me, I said something offensive and hurt the poor thing's feelings."
Star and Marco exchanged shameful looks before they sighed and turned away. Then, after a while, Marco asked, "Hey Star, would you like to do doggy style with me?"
"No, Marco, I don't want to make you go through the same pain I went through."
The princess then heard a zipping sound and turned around to see Marco take off his pants and panties. "I insist." He uttered as he blushed and gave Star a flirty look.
Star blushed as well and laughed before answering, "How can I say no to that face?"
So, with their idea set in mind, Marco went to his bed and got on all four as Star got ready to perform the doggy style...without lubricant. They begun, and it played mostly like the first time: Star went inside a bit too fast and Marco tried to hold the pain. However, unlike last time, Marco managed to withstand the pain just long enough for Star to cum, and then it played like the first time as Marco shrieked "Pull it out!" and Star obliged.
Along with the blood, some sperm came out of Marco's asshole as he cried a little and caught his breath. "Did I hurt you, Marco?" Star asked worriedly.
"No, don't worry, It's okay." Marco lied as he struggled to get up. "The sperm somewhat helps with the asshole pain, though I have no idea how the hell that makes any sense."
After that, Marco and Star swapped back to their original outfits before they exchanged small smiles. "Well, time to change the genders I guess."
Star took out her wand, used the same spell as before and changed both her and Marco's gender back to their original ones. After that, Marco felt the pain of his asshole was gone and, seeing that it was 7:55, bolted out of the room as Star waved goodbye...while some blood and sperm went down her leg.