Disclaimer: I do not own rick & morty
A week had passed since Summer had kissed Morty, and he was keeping his distance hoping whatever had caused her to do that would fade, he took his dinner's late, he was going on more adventures with Rick than usual, and he was trying his best to be out of the house, After the incident in the other reality he didn't want to have anything to do with this stuff, not for a while anyway, stupid brain chemicals why did they have to turn his sister's feelings like this? He wish he knew.
Rick was glad to see morty focusing on his education and science in general more than usual, whatever had happened between his two grandchildren it's good that Morty was doing everything he could to stop it, Rick knew deep down that things would be bad if things had progressed further, not only because of the detrimental affects of inbreeding, but because of the quantum variances between the two realities, realistically he wasn't exactly sure what would happen, but it wouldn't be good.
They stepped through the portal a pair of eyes watching them through the door, suddenly Summer rushed out shoving them through and fell in after them, she was obviously not thinking straight, rushing into a dimensional portal like that was dangerous when you knew where you were going, but what if because of her actions the portal maker was damaged trapping them here, it's not like this dimension was known for it's technology.
Rick glared at Summer then shrugged it off there wasn't much he could do now and he could use an extra pair of hands anyway, the trio wandered both Morty and Summer were silent, the tension in the air was so thick not even a plasma sword could cut it, finally Rick told them both to wait there while he got what he came for, it was only a short walk from there now and he would be back relatively soon
the two sat on the ground in silence, a ringed planet in the sky indicating this was a moon rather than a planet they were on, Summer was the first to break the silence "Morty why are you avoiding me?" he looked at her with a look of dread on his face, he really didn't want to answer that "be-because you... I don't know what you want bu-but I cannot provide it I think" she looked at him shocked, is there something wrong with caring about your little brother? "n-no but you kissed me, I think tha-that's a bit dif-different" she looked hurt he wanted to comfort her but he was afraid of sending mixed signals right now.
He wanted to tell her about how his selfish desires had destroyed their own time line but she probably wouldn't understand, did she even know who Cronenberg was? While he was quietly debating what he should do she moved closer to him, he didn't notice right away until she was practically on top of him, realizing this he took some steps back he looked at her again she seemed different, her eyes seemed empty, almost like she wasn't herself "Su-summer?" he continued to look at her, she seemed rejected almost "lo-look Summer I just can't ok? It's a very bad idea, you're my sister, remember?" she seemed to think about it for a second then a smirk appeared on her face.
Her thoughts continued to go to him, yes he was her brother but he also wasn't, and she didn't know enough about realities to say why but she felt something for him she shouldn't she just continued to get closer until finally he was backed up against a cliff face she took this chance to pin him until she sad what she wanted to say "listen Morty, brother or not there's something different about you, and I don't think I can go back to just thinking of you as my brother, not now, I feel... different with you around, not even Ethan makes me feel this way, and I want to pursue it I don't care how, I'm sure grandpa Rick can figure out something if it comes to that but damn it I want you not some scumbag ex boyfriend." she was starting to raise her voice when she stopped, she realized what she had just said, had she just confessed an attraction to her brother? This thought snapped her out of it and she backed away running back towards where they were supposed to meet with Rick before returning home, she returned there to find him waiting.
Rick was looking around wondering just where his grandchildren had wandered off to, only to see Summer running over a hill with Morty following close behind, Rick just opened the portal and all 3 went back home, the two siblings quiet again, Morty seemingly more confused than before and Summer deep in thought, he knew what was going on, and he didn't like it, he was going to have to do something to stop it, or at least to take the risk away.
That night Morty was trying to sleep when he was startled awake by Sumemr by his bed, she seemed concerned, she motioned for them to go for an evening walk so they could talk in relative privacy, as they stepped outside Summer donned a hoodie and Morty a large coat his grandfather had gave him after one of their adventures in a colder dimension.
He looked at the moon it was full and covered by the clouds, the stars not visible, it might rain soon, then he looked at Summer who seemed to be thinking about what to say when Morty spoke up "su-Summer listen, I know this must be hard but you and I can-can't happen do you un-understand?" she seemed distracted as she watched him, her eyes taking on a slight lidded appearance "Su-Summer do you understand me? It-it's a very ba-bad idea, and we are t-too young, well you aren't b-but I am."
she just watched in silence, her mind filled with thoughts of him, she was distracted, she knew something wasn't right but she wanted him to kiss her again, it felt so good before she wanted to feel it again, she knew about the rules but she didn't care, he wasn't really her brother right? He seemed unsure of himself a flight or fight response kicking in as she grabbed his arm she gripped him firmly but gently feeling him give in as he didn't want to hurt her, she placed her lips on his and felt the rush of sensation enter her mind again, the warmth filling her body as it had before, why did he make her feel this way? This other Morty, it was strange but she felt rebellious at that moment, like she was going to break all the rules and didn't care.
she dragged him back up to the hill where they were before, he had stopped resisting, his eyes seemed empty, almost in shock, a stunned silence on his face, he had internalized himself, she waited for him to snap out of it before holding him closely "see Morty this isn't so bad is it?" his breathing was slow but his heartbeat was fast, the fluttering making her own heart beat in time with his. "S-summer please we have to stop, i-it may feel good now but there are se-serious consequences for our actions and I don't just m-mean the legal and social rep-reprocussions" that nervous stutter again, she had grown to like it a lot.
He didn't know what to do, he felt trapped but it wasn't unpleasant, he felt torn between being a good brother and whatever his body was screaming at him to do, he tried talking her out of it but it seemed to fail, she was too intent on doing whatever it is she was thinking of doing, and it made him uncomfortable, the feelings of good and bad causing him to just continue being confused as he was having trouble sticking with his decision to resist, he wanted to scream for her to stop, but he didn't want her to stop either, it was bad, but yet he enjoyed it, the feeling of electricity when she put her lips on his, it reminded him of Annie, who was inside her ex boyfriend now re-building anatomy park, oh the irony.
She pulled him in closer, the darkness hiding them from the public eye, his eyes growing tired because he hadn't gotten enough rest before she woke him up, she pressed his head against her chest, he could hear her heart beating beneath her firm breasts, soft but comfortable some how, her body warmth lulling him into a deep slumber.
As she felt his breathing slow she realized he had fallen asleep in her arms, some how she felt excited about this, she felt that warm sensation again and began to carry him back to the house, she then tucked him into bed kissing him on the lips one last time before heading to her room so she could rest herself, unbeknownst to both of them though Rick was watching from his flying car, he wasn't happy but he knew that they would have to work this out for themselves, until then he would have to keep working on his latest project, something that if problems should arise should resolve the issue.