Based on the memory parasite episode. Warning: Very violent towards the end
You had gone to Morty's house to goof off with him, he had told you he had gotten the new Pokemon game and wanted to show it to you. Push went to shove and you ended up having to sleep the night since your parents weren't able to pick you up and Morty had always been the best person to help you fall asleep since you had some pretty bad insomnia. So it was the next morning, and you were eating breakfast with Morty and his family. Morty's Uncle Steve was there with them. They were laughing about experiences they had with with him. You sat there in confusion, you had never had any of these experiences. You made the face as you simply ate your breakfast, trying to be polite and laughing along. Eventually Steve told them that he was treating them all to a vacation, as you muttered a soft 'Lucky you guys.' under your breath.
Rick walked in after throwing away some glowing rocks in the trash, beginning to bicker with Jerry about them. Rick asked who Steve was and just as you were about to say 'Yeah who is he?' Rick pulled out his intergalactic pistol and shot Steve in the head. The entire family except you and Rick panicked as they stared at the dead body of 'Steve' who shriveled into a parasite form. Later on you were all in the living room, Rick had put up the blast shields and wrote down a big '7'.
Eventually, they had all multiplied, they was so many the house was practically filled to the brim with zainy people. Later, everyone was beginning to get very suspicious of Rick. Morty glared at him and had him escorted to the garage, while you followed out of concern for Morty possibly shooting Rick. You begged Morty not to shoot, biting your lip in concern. "Stay out of this, (Y/N) if-if you're even real," Morty said, giving you a glare. Morty soon realized you could only form good memories with the parasites, killing the two that had brought Rick in.
"Now how do I know you're real, I don't think I have a bad memory of you," Morty said, glaring at you as he pressed the cold barrel of the gun to your forehead. You were down on your knees begging for your mercy, hot tears of horror streaming down your cheeks. "M-Morty ple-ease... I-I.... I-I lo-love you..." you sputtered out between sobs. He glared a little more as he tried to remember anything- anything bad. As mean as he looked, he prayed you were real, he wanted you to be real. He breathed a sigh of relief, scaring you as he gave you a calm smile.
Morty pressed his lips to your own, giving Rick the gun and pulling you close. A few moments later he pulls away, smiling, "You're real... Rick pants-ed me when I was trying to ask you to be my friend. I l-love you too." You laughed softly, the memory of his unicorn chaser boxers still burned into your brain. The three of them decked each other out with intergalactic weapons, busting in. After every parasite was killed and everything was over, everyone was ready for dinner and started eating. Beth gave you a dirty look, pulling out one of the intergalactic pistols and shooting you in the stomach. You were shot back, slamming against the wall and sliding down it, leaving a massive splatter and streaks on the wall of blood. You were too stunned and in pain to cry. "What the hell mom! You-you just shot my girlfriend! O-Oh man oh geez..." Morty shouts at his mom. Jerry was reporting a shooting to 911 as Your vision started blurring, everyone rushed to your side. Beth ran to the kitchen and you sat there, struggling to keep from passing out. You hurt all over, looking up at them with a pleading look. "(Y/N)- No no no, babe please don't go to sleep. It's okay you-you'll be okay. Just don't go to sleep, look at me please" Morty said waving his left hand in your face as he gently caressed your cheek with his right. You spluttered out, coughing blood. Your chest hurt, you started crying softly, "I-I don't wan-*coughs* wanna die..." Your vision finally went black as you passed out from the blood loss.
*timeskip*
You woke up in a hospital, the blinding like hurt your eyes. You tried to sit up, but the pain caused you to stop. You had bandage wrapped around your lower stomach with a blood spot where you remember getting shot. Your parents understood that it was all an accident and decided not to press charges upon Beth. Morty was to your side, fast asleep. You gently shook him to wake him up. He yawned and blinked, staring at you for a moment before smiling, tears pricking at his eyes before he leaned over and gently hugged you. "Oh-Oh my god, (Y/N) I-I thought you wouldn't wake up!" Morty said happily, pulling away. The rest of his family walked in looking at how you were up and smiling. It was a happy reunion as they gave you little trinkets. Morty smiled at you and pecked your cheek, blushing awkwardly. He was surprised to feel your lips upon his but he eased into it anways, allowing you to wrap your arms around his neck whilst he placed one hand on your face and the other on your side. You two split apart and laughed, sighing softly.