After reaching the surface, Frisk had decided to stay with Toriel. Of course, she had no problem taking in the child but not everyone was so taken with the idea of Frisk being alone with such a kind being. Sans was the one who offered to help Toriel getting settled on the surface once again after being so long, using the guise of her helping him adjust to life on the surface as an excuse.
Soon after, Chara was brought back with the help of Doctor Alphys.
By that time, Sans had decided that Frisk could've been left with Toriel with no problem, but after the events proceeding the most recent timeline, he couldn't leave Chara on their own with their mother and the child that drove them to such lengths. He offered once again to stay, and Toriel didn't refuse him.
Another week passed and Chara proved to be no problem, or at least not a huge threat that he needed to watch 24/7. He was silently making plans to leave but another member of the house joined after a somewhat extended stay before hand.
Asriel was given a body by Alphys in a way similar to Chara's revival. Of the three, he seemed the most stable, but Sans was worried about the kind monster's sanity of readjusting to the surface and taking care of three children at the same time. The skeleton decided to extend his stay once more.
Over the course of providing help around the house and whatever chores he could help with in town, Toriel and Sans had started becoming closer. They had a bond from the Underground, but becoming roommates with someone and putting up with the outrageous things that the children, usually Asriel and Chara, happened into, brought them closer.
After a particularly long day, Sans had walked out of his and Papyrus' room. The short skeleton lifted his arms and stifled a yawn. Long day… He made his way to the kitchen, to see Toriel at the stove. "Oh… Hey, Tori. You making a snack, too?"
Toriel smiled towards him. "Well, yes, but it is not for me." She giggled a bit as he looked confused. "You have been such a great help these past few weeks… I thought you might like something special as a reward."
"Aw, really?" Sans rubbed the back of his head, his face flushing blue from the gesture. "You didn't need to do that… But I won't turn it down." He raised his hand to bring the plate of snacks to him, but the goat monster took the plate in a tight grip. "If it's mine… Why aren't you letting me have it?"
Toriel gave him a somewhat stern look, though a hint of playfulness was hidden within. "Sans, you are not hiding in your room like you usually do. You may have these treats, but you have to sit with me and eat them."
Sans shrugged, smiling a bit. "You really got my goat, Tor… Fine, you wanna watch TV?"
Her expression softened instantly before she giggled at the lame joke. "That sounds fine. Do you mind a cooking show? There is one I have been following that is premiering a new episode tonight."
He was already heading to the living room, motioning her to follow as his response.
As the first show ended, Toriel looked to Sans, a sweet, hopeful smile on her face. "So, it was enjoyable, was it not?"
Sans had long finished his plate of food, his finger absently tapping the plate as he watched the end credits. He glanced over at Toriel, his hand resting. "It was pretty egg-citing." He brought his arm up to rest on the side of the couch, a wide smile growing across his face. "Can't wait lentil the next one."
Toriel fell into a small giggling fit. "Orange you glad I talked you into this?"
"You breader believe it," He started snickering. He grabbed the remote and checked the guide. "Next one is-"
Toriel grabbed his hand excitedly, smiling as she started to go on about the show. "It is almost like a guessing game, but much trickier. Actually, Papyrus might like this one as well. The object of the match they record is to see who is the professional chef and who is the pretender. It's quite enjoyable."
The sudden contact held Sans in silence for a moment. His face turned a bright blue as he debated pulling his hand away. He decided against it for a reason he couldn't place. "Oh, yeah. Compared to the one before this is way different." He cleared his throat, somewhat embarrassed of the way his words were choked out before. "Should be a-peel-ing." He smiled at his own joke before settling back to watch TV.
Toriel giggled, resting her hand back in her lap as she began to watch the introduction to the show.
After the show, Sans sat smiling somewhat smugly while his companion pouted. "I still think you had some reason other than 'a lucky guess.'" She gently poked his cheek as she mocked his voice during the last portion of her sentence. "There is absolutely no way you could have guessed all the fakes when they used such professional techniques."
Sans started chuckling, his face flushing again from her admittedly cute behavior. "What can I say? I got a sub-lime sense when it comes to sniffing out fakes."
"I am going to have to draw the lime there, Mr. Skeleton." She poked him again before lifting him to be eye level with herself. "Your saucy behavior will ketchup to you one day." She teased. She had intended to threaten him, but the silly expression he was making had caught her off guard.
He poked her muzzle with a wide grin, his face still a slight blue. "I cannoli tell the truth. When it comes to impastas, I'm on my game."
"Oh please," She tried to suppress giggling as she spoke. "That was a bit out-dated, do you not think?"
Sans didn't respond, a certain term she used clamming him up. When he didn't respond she looked at him with concern. "Sans, are you okay? I'm sure you've got a few more jokes. Are you tired? Have I kept you up too late?"
Sans nodded. "Say… Um, knock knock..." He had to clear his throat, his voice starting to betray him.
Toriel looked at him, her head tilted slightly. "Who is there?"
He nearly melted from her confused look. Her expression coupled with her ears slightly flopped to one side shut him up for a few seconds as his face brightened in hue. "Olive..."
"Oh? Olive who?" She smiled a bit, not exactly knowing the answer but happy to continue the joke session.
"I… think... Olive you…?" Sans rubbed the back of his head.
"You think..." It was her turn to blush. "Oh, Sans… Are you being serious right now?" She began to smile in a mixture of being happy and flustered.
He nodded, smiling a bit. "Y-yeah? That a problem?" He grunted before laughing as he was squeezed tightly. "Is… that a no?" He was still flustered but not being rejected leveled his voice a bit.
"Of course it is not!" She tried to keep her voice hushed due to everyone else in the house being asleep. She giggled. "I'm so happy you told me." She squeezed him once more before sitting him on the couch.
"So… You'll be my girlfriend then?"
"Of course," She smiled happily. "Nothing would make me happier."
He smiled, resting against her side. This gesture wasn't foreign. He often did this when he was tired while they watched TV like this, but this time, in particular, made him especially happy.
Toriel smiled, putting her arm around his shoulder as they continued to watch TV.