Sans is a MONSTER and not a HUMAN, so he doesn't follow HUMAN biology like a HUMAN skeleton. Same with Gaster and Papyrus. 

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Almost 7 years. That's how long it has almost been since Sans and Frisk had been together as a couple. The fact that that much time had passed was quite insane to both of them, and that was made even more evident whenever their anniversary came along. The skeleton always made an effort to try and never forget whenever their anniversary was, just because it meant as much to him as it did to her, (not that he thought that people who forgot didn't care or anything). But usually it was just expected of the guy to forget, while the girl always remembered. Not in this relationship though.

On some anniversaries, the two of them went out to eat somewhere. A couple of times they had gone to the same place where they had eaten at for Frisk's 20th birthday, seeing as the place had a really nice, romantic atmosphere. And it held such a wonderful memory that the two of them still hadn't forgotten about. Those were nights that Leo and Luna would get babysat by one of their friends, or a member from Sans' family. 

That, or if the two weren't really feeling a night out, then they would simply stay in, have Papyrus, Mettaton or whoever they trusted in their group take care of their children, and they might have their own cooked romantic meal, or just enjoy a couple of movies together and that would lead them wherever. Their dates were always sweet on their anniversaries, no matter what they were up to. Though, Frisk was thinking, she wanted to try and make this upcoming anniversary the best date they had in awhile, for one big reason. 

She was thinking of asking Sans to marry her.

Question was whether she even felt like she could do such a nerve wracking thing. When she even thought about it, it made her somewhat understand why Sans was so fearful of such a thing, (though, he was probably a million times more scared than she was). Part of her just thought about waiting around to see if Sans would eventually gain the strength to ask, and it wasn't like they had to get married. It wasn't the most important thing in the world. Nothing was more important to her than what she already had. 

However, she knew she couldn't deny that it was something that she did want. No, it wasn't the most important thing, but... She could almost smile at the thought of seeing Sans in a nice, tidy suit, waiting for her with a grin, maybe at the end of an aisle or something. She would be wearing a long, flow-y, elegant white dress, with her hair all done up... She would hardly be able to stop her lips from being pulled into the widest smile ever, knowing that everyone would be beaming back at her. Her children would look so utterly adorable in their little outfits, and she knew it would be a day she could never, ever forget. 

But then her heart sank a little. What if Sans didn't want that though? What if he ended up saying no because marriage was just too much for him? She didn't want to scare him... The worried expression must have been pretty evident on her face, because she was brought back from her worrying thoughts by Gaster. Her and Sans had actually come back to the town with their two children, and Sans was currently likely with Chara and Asriel with the two little ones, playing in a park somewhere. 

"Someone is looking concerned." Gaster teased, which what caused Frisk to weakly smile. They had currently come to a stop on the sidewalk, and were standing literally right outside of the place Frisk had asked Gaster to show her - the jewelers shop. That was why she was currently separated from her skeletal boyfriend, as she had wanted to come here to see if she wanted to get a ring. "Having second thoughts?" He asked, which Frisk wasn't sure how to answer. She wasn't really sure right now.

"I don't know..." Frisk sighed, staring in through the window at all the nice rings she could see through the glass. Would she see one in here that made her think: yes, this makes me think of Sans? "I just... I know it's something I want. I want for us to be married, and I don't know if Sans will ever be able to be the one to propose... I just don't want to scare him away." Frisk admitted quietly, linking her hands together behind her back, due to the nervousness that such a thought made her feel. 

"I don't think you will scare him away, Frisk. Of course, I know how Sans has been a bit of a nervous skeleton over the years... However, he clearly cares a very great deal about you." Gaster mentioned, noticing how Frisk was listening, with that thoughtful expression upon her face. The skeleton smiled. "I'm sure the two of you are ready. But if it is something you really want, then one of you has got to make the move. I know how nerve wracking it can be, believe me." 

"Says the one who has done it twice." Frisk teased, hoping that her joke didn't hurt the skeleton's feelings. Thankfully, it didn't seem to do so, and he only chuckled at her tease with a grin of his own. But what he had said did make her feel somewhat relieved that despite having already done it once, he still felt really nervous having asked Grillby to marry him. It made her feel less alone and anxious about it, only by a little bit. But it was at least better than nothing. Okay... She could do this right? "Let's go in." Frisk finally said, pointing towards the door, and the monster nodded, going to follow into the store after her once she had decided to step inside. 

Frisk was almost left in awe when she stared around the store, seeing all kinds of beautiful jewelry; all those amazing, glistening rings. Would she even find one that was right for Sans? She wasn't sure. Surely though, it was worth a look, if she was even thinking of going through with this. Eventually, her feet finally began to work, and she went to peer around at all the different kinds of rings, but a lot of them didn't really feel like one she would give to her skeletal boyfriend. They either looked just... Weird, ugly, or not fitting. 

But then she saw one that caught her eye - a ring with a red gem. She knew Sans' magic colour was usually blue, but the colour of her own soul she remembered as red, from all the times she had actually been able to see her own soul. Would it be sweet to propose to him with a ring of her colour, or would that just be insanely cheesy? The thought sounded quite cute to her though, so she was close to considering it. "See one you like?" Gaster questioned, being at Frisk's side as he said that, and she nodded. 

"I think so." Frisk murmured, thinking over in her head whether or not she wanted to do this. Whether or not Sans would actually say yes. He would, right? He might have been nervous about marriage it seemed, but would he really say no to her? She didn't want to think so. So, she firmly decided that she would buy it, before she would choose to try and back out. She wanted to get this ring right now, before anyone else would try to buy it. 

And when she was walking out of the store with an actual little box with the ring inside of it, it was difficult not to be lost for words at the fact that she was actually considering this. Yeah, she always imagined when she would be in a relationship with the person she loved, that they would propose to her. But she didn't really care about that anymore, just the thought of Sans' reaction and him saying yes to her was all she needed, alongside the wonderful day they could have for their wedding. 

"It's a nice choice." Gaster said. "I'm sure he'll like it." He continued, as the two of them started to slowly walk along the sidewalk, and Frisk continued staring at the ring in her hands, at least until she finally closed the box, and went to put it away in one of her pockets so she could hide it later. She beamed widely. 

"...I think so too."