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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Husband and wife... Ready to go on their honeymoon. How insane was that? It felt like it had taken the two forever to actually pack everything that they had wanted to take, but when all was ready, it felt extremely worth it.

Where were they going? Well, at first, neither of them had actually been entirely sure where they would want to go for their honeymoon. There was all these places they could travel to, like Paris, Italy, Hawaii... Typical places people tended to go. It did sound romantic to be able to take a picture in front of the Eiffel tower at night, but neither of them were even sure they wanted to go to Paris.

"Why don't you go on a cruise?" Chara had suggested to the couple, while they were sitting in Grillby's bar. The flame monster serving drinks had shuddered at the thought of being completely surrounded by endless amounts of water, while Sans and Frisk on the other hand, had thought of considering the idea. Neither of them had really been on a boat before, (which did make Frisk a little nervous she'd get sea sick), but it would be the real only chance to see what it was like.

So, that's what they had decided. That they would spend their honeymoon together on a cruise. Frisk had her fingers (and toes) crossed that she wouldn't end up getting sick during their time together, otherwise that would really ruin the romantic atmosphere, her being sick over the railing, into the sea.

They were lucky to have good friends and family, who would offer to look after Leo and Luna, like Papyrus and Mettaton. Sometimes they would be babysat by their grandfather - Gaster, or their aunt Chara, but most of the time, it was Papyrus and Mettaton, only because they lived closest, (and were great with the twins).

"We're going to miss yooou!" Luna was saying to their mother and father at the door, wanting to hug each of them tightly. Leo wasn't any better, joining in on the family hug, while Papyrus and Mettaton were smiling widely, finding the group so utterly adorable. Sans and Frisk chuckled.

"We'll only be gone for 2 weeks. We'll be back before you know it." Frisk lightly told the two, while Sans was nodding. The small boy pouted, having a thoughtful expression upon his face, as if he was trying to work out how long 2 weeks were. In fact, that's exactly what he was doing.

"2 weeks, so... one, two, tree... four..." Leo tried counting off of his fingers. Once again, Frisk giggled.

"14 days, kiddo. ya can count them down with your cool uncle, so ya don't lose track." Sans teased, going to ruffle Leo's hair, while also smiling towards Papyrus and Mettaton who beamed in return.

"We hope you have a safe trip, darlings." Mettaton said. "And have a good time." He added, of course having to add a wink in at the end of that sentence, causing Sans and Frisk's faces to go bright blue and red, like dazzling fireworks on the fourth of July. Clearing his throat, Sans spoke up.

"thanks, we will..." Sans murmured, meaning that in the most innocent way possible, but he could already tell from the robot's smirk that he and Frisk were going to spend their 14 days alone together, celebrating their marriage in a certain way. Because to people, that's what honeymoons were about, right? Not necessarily... Not to say it wouldn't be like that at all, but... There was a lot more they could do than just that for 2 weeks. They were going to be on a cruise. Might as well enjoy it.

When it had arrived, Sans and Frisk finally took their leave after saying their goodbyes, and got into the taxi that they had called moments before. When they had sat inside the vehicle, it was difficult for them not to smile at each other excitedly. Sans went to grip onto Frisk's hand that was closest to him, which was her left hand, seeing as she was sat on his right, and he gave her hand a gentle squeeze.

"i love ya..." Sans murmured.

"No, really?" Frisk teased with a giggle, causing a low chuckle to erupt from the skeleton. "But I love you too. I always thought having two children had been crazy enough. Sometimes it is still mind blowing. But it makes my heart feel so full, now that we're actually married, and about to go on our honeymoon." Frisk said.

Sans knew he couldn't agree more, as they held hands all throughout the car journey, while continuing to smile from ear to ear about their honeymoon. Though, Frisk couldn't help but grow increasingly nervous, the closer they got to where they would have to get out of the car and board the cruise, just because she was worried she would end up being someone who would be sea sick, and then she would ruin the whole 2 weeks for the both of them. The skeleton must have noticed her anxiousness, because once again he squeezed her hand.

"shouldn't it be my job to be the more nervous one?" Sans told her with a grin, as any time it was the other way around, he couldn't help but jokingly poke at her for it. It made any situation more light-hearted. It was better than doing his usual job of making things feel more cynical or worrisome. Frisk smiled.

"Sorry. It's just hard not to be nervous, I've never been on a cruise before. But I'm also excited."

"i know. i feel the same way." Sans lightly told her, just as the car came to a stop. That being said, (which definitely made Frisk feel more comfortable), the pair climbed out of the car, making sure to bring their bags with them. Linking their hands, the married couple started on their walk towards the cruise ship, where they could go through the whole process of boarding, and going to find their room.

"This place is massive." Frisk had gasped, when they managed to find their room, and place their bags down beside the bed. The room was extremely clean and neat, which was good. It would be horrible to turn up in their room, to find it was a mess.

"to be expected for a cruise ship i guess." Sans said. Again, Frisk beamed, and went to walk over to her husband, where she linked one of her hands back within his. She stared right into his face, right into those two  sockets of his, that stared softly in return back into her own two blue eyes. Inching her own face closer to his, she placed a loving kiss against his mouth, which he of course didn't even hesitate to return. In fact, he went to put one of his arms around her waist, only to pull her closer. It made him so happy that they'd get to be alone together for the next two weeks. Not that he didn't enjoy the company of others, but... They were just able to be romantic around each other without having to fuss over anything else.

"How about we go up to the deck, so we can see the ship start to sail away?" Frisk suggested, keeping her hand linked within her husband's, who seemed to agree with her suggestion. With that thought in mind, Frisk lightly tugged on his hand, so they could make their way to the deck, just like she said.

When they got to the deck, Frisk was actually the first to smile widely, like a little kid, as she ran towards the railing, so she could lean her arms upon it, and stare out to the place they were already starting to leave behind for the next 14 days. The ship had started to move. Coming up behind her, Sans stood close, putting one hand on the railing, while one hand was held in the middle of Frisk's back, like he was ready to protect her at a moment's notice. Frisk beamed, feeling the wind starting to blow through her hair, being able to smell the smell of the salty sea... She turned around to face Sans, who looked just as happy as her.

Once again, she went to press a gentle kiss to his mouth, before hugging him tightly, causing him to also hold her tightly in return, in an affectionate embrace. They could hardly wait to spend the next 14 days together.

It would be a fun honeymoon.