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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In the morning, the skeleton woke with a bit of a groan, due to the fact that he could hear the sound of what sounded like blasted ringing beside his skull. When tiredly blinking open his eyes, it wasn't difficult to notice that the sound was obviously coming from his phone upon the desk beside their bed. Sighing, Sans reached for his phone, wondering who the hell was calling at 6am. He hadn't planned to wake up for another hour. He could only grumble, seeing that the caller was Chara, especially when he could hear the sound of Frisk shuffling awake beside him. With a yawn, he answered and put the phone beside his skull.

"what?" He spoke quietly, both because he was sleepy, but also because he wanted to try and let Frisk drift back off to sleep so she could get some extra rest. She had been pretty busy at work yesterday after all, so he wanted to give her special treatment and let her rest for a little bit longer. "what do ya want, chara?" He sighed, before putting an arm around the human who had started to snuggle up against him after being woke up. He softly kissed Frisk on the head, before putting his attention back to the phone.

"Sorry, I can tell I've woken you up. I was just calling you to tell you you should probably come in to work today." Chara mentioned, and when Sans questioned why he would need to do that, and why her telling him that required her to call him at 6am, she continued. "Asgore says he wants to talk about something, to everyone. He told me to let you know because apparently he thinks I have an easier time of convincing you to show up." Chara explained, shrugging her shoulders, despite the fact that Sans couldn't exactly see her. So, was this some kind of meeting then? If it was directed towards several people at once, he knew it must have been important. "I'm worried." Chara said. 

"huh, why?" 

"Because I have a feeling I know what this is already about." Chara told him. She just hoped that she wasn't right. What she was thinking that maybe Asgore was going to step down from being the Mafia's boss, and that could only mean one thing, that the Mafia would choose to close down. She knew he would probably do such a thing because he wanted to spend more time with Toriel, he had been making more of an effort to do so after all. However, no one would gladly take Asgore's position to do what he did, as being the boss of such a group must have been not only such a time consuming thing, but also stressful. 

Back in the day, if Asgore was ever going to step down, the most likely people that Chara could have ever seen being the next boss was Sans, or Gaster, just because they seemed like likely candidates. Like they could just handle such a difficult task. That wouldn't be the case now though, with the fact that Sans had Frisk and his kids, and Gaster was just getting on with his life with Grillby, and  they would eventually be getting married. Neither of them would want the position, and Chara knew she herself wouldn't want it. It would be too much. 

"Just get down here, okay?" And that was all Chara said as she went to hang up. Sans looked at his phone screen in bewilderment, but sighed as he decided to sit up and stretch, knowing he was going to have to pick himself out of bed then. He knew he didn't want to go, but if this was apparently important, then he probably should. He was actually just getting dressed when Frisk appeared to wake up more, and she sat up in bed with a yawn of her own.

"I want to come with you." Frisk said, earning an eyebrow raise from Sans. "I heard what she said - she said it was important." And if it was important, she wanted to know what was going on, but when Sans shook his head as if to say no, she could only ask why. He sighed.

"frisk, ya aren't part of the mafia anymore. ya don't have to be worried about whatever it is about. it's probably not even that big, and i can just tell ya when i get back." Sans told her, but to her that didn't seem good enough. He knew she would probably still have some attachment to the group, even after leaving it, not necessarily because of the missions she went on, but because it meant she got to see Chara, Asriel, Andrew... Yeah, they visited now and again, but you were definitely able to see them a lot more often if you were working at the Mafia. 

"I want to see everyone too. Please?" Frisk pressed, only for her fiance to wonder: what about the kids? Because if he was going to go, and she was going to go, it meant they were going to have to get someone to babysit them while they were gone, and take them to kindergarten. He knew no one had any problem with that, that Papyrus and Mettaton could easily do that, but... He just didn't want to take Frisk with him. But when she was bugging him to go, and giving him that puppy eyed look, he hated that he found it harder to put his foot down. She did say she wanted to see everyone, and he didn't really want to stop her from doing that. It wasn't like she was going to get involved again, so... 

"ya can come. but that doesn't mean you're suddenly involved again." Sans told her, while Frisk replied, saying that was just fine, while she climbed out of bed and proceeded to join the monster in getting dressed herself. When Sans was completely dressed, he went to dial Papyrus' number, so he could call him to babysit Leo and Luna. He was relieved when the brother didn't seem to mind whatsoever, and he gladly accepted his request. When Papyrus showed up at the door, (with Mettaton too), Sans and Frisk thanked the two for their kindness. 

The entire drive, Sans couldn't help but wonder what the hell this whole meeting would be about, and why it was supposedly so important that he had to show up. But he didn't want to miss out on information that might actually affect him in some sort of way later. He could tell that even Frisk was pondering as to why Chara felt it was such a big deal to call about this meeting, but they would very likely find out in just a second, when they arrived outside the alleyway that led to Grillby's bar. 

It was the same process of saying hello to the flame monster, before proceeding down into the elevator. When the elevator reached the bottom, and the doors slid open, the couple couldn't help but notice all the monsters standing around, while they noticed Asgore standing at the front of the large crowd. Stepping out of the elevator, Frisk glanced around to try and spot some familiar faces, only to find Chara and Asriel standing together, near the front. Pointing them out to Sans, the two proceeded to push past the couple of monsters, to finally reach the other human and the goat. 

"Oh, Sans, you actually got here. And Frisk? What are you doing here?" Chara questioned, but despite asking such a thing, she didn't seem bothered that Frisk was here. In fact, she gave the other girl a hug, and Frisk could only laugh a little and happily hug her in return. 

"I heard something important was going on, so I felt like tagging along." Frisk explained. 

"Sorry to gather you all up on such a sudden notice." Asgore spoke up, while everyone began listening carefully, especially Chara, Asriel, Frisk and Sans. "I brought you all here to let you know that... Well... I have decided that I am going to be stepping down." He explained, and it was then that Chara hissed under her breath, commenting about how she knew it. Hearing that, Sans himself wasn't quite sure how to feel, and when he glanced towards Asriel it seemed he too was surprised. "I know this might seem a little out of the blue but... It is not. Because I am sure no one else will resume the position, the Mafia will be closing down." 

"wow..." Sans breathed. He didn't even know why he felt that bothered, it's not like it really mattered that much, did it? After all, he didn't really come here as much as he used to anyway, as he had been wanting to spend more time with his family. In fact, he said that if he had to quit at a moments notice for his family, he would. So, why was he so affected by this? Was it just the shock of knowing that something he had been a part of for so many years was just going to be gone? That was probably part of it. He knew he wasn't the only one who was bothered though, seeing as it wasn't difficult to notice the fact that others began whispering and muttering among themselves, looking nervous and displeased. 

"You can't just do that!" Chara decided to speak up in annoyance, knowing it was inevitable that saying such a thing was going to get many eyes looking at her, but she didn't care. "A lot of people's livelihoods depend on this! And we're like... A family!" Chara complained, for some reason finding herself a little emotional at the idea of losing the Mafia. It had been a big part of her life, especially hers and Asriel's life. She didn't want to just lose it. She knew Asgore probably wanted to quit so he could spend more time with Toriel, but... "Surely, there's got to be someone who will take your position! Right?" Chara went on, and when she said that, people once again began whispering and glancing at each other, as if they were waiting for someone to speak up, to answer her questions. But it remained pretty much silent, and Chara looked ready to lose hope. At least, until someone answered, but when this person answered, it was no surprise that a certain skeleton was going to give her a look as if she was completely insane.

"...I'll do it." 

Frisk.