Sans is a major character in the Over the Void comic series of Undertale. He was once the former assistant of the old Royal Scientist, W.D Gaster. After briefly appearing a different world where monster and humans are at war on the surface, Sans now has blood inside of him while his soul is now filled with Patience. He is the only monster besides Alphys to know of the Amalgamates before they were sent back to their families.
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Sans is a skeleton that was presumably born in Snowdin of the Underground. He was napping at his sentry station when he received text messages from the current Royal Scientist, Alphys, who wished to talk to him at her lab in Hotland. Papyrus then came along before he could use his shortcut and shared his run in with Doggo, and compared it to be the same with all the other Dog monster stories. Papyrus continued on his way, and Sans then used his shortcut to get to the lab.
He was greeted by Alphys, who was surprised by his immediate arrival. The two sat down and ate Ramen as Alphys asked questions regarding his past as a scientist. Sans confirms he was once a scientist under the employment of the original Royal Scientist, but can vividly recall his past and who the old scientist was. Alphys began to hand him his old folder, but began to have a nervous breakdown, so Sans told her a joke to calm her down, causing Alphys to slowly warm up to him and act more confident towards him. She proceeded to hand him his old and burnt folder and explains that some of the writing was something she didn't know how to read. Sans could read this font perfectly fine. As he began to tell her the name of the font, Sans opened the folder and was immediately alarmed by some of the sketches and burnt marks making a creepy face that seemed familiar to him. As Sans began to break down while recalling his past, he heard noises coming from the elevator. Recognizing the voices, Sans ran down the stairs and into the elevator, despite Alphys's objections.
Arriving at the True Lab, Sans explored while remembering it's original state, until arriving at the DT extractor. As he kept recalling more bits of his former life, he was greeted with a rather warm welcome by Endogeny and the other amalgamates, who seemed to already know he he was. Alphys ran into the room, and broke down crying since Sans now knew the truth of her faults. Instead of being disgusted by her actions, Sans consoled her and offered to take her back upstairs, as he had something to share with her as well.
A while after the barrier in which sealed monsters under Mt. Ebott was broken, Sans was napping under a tree, dreaming of his first time meeting Alphys. Then he was woken up by Frisk, Asriel, and Monster Kid, who wanted to go back to Snowdin the next day since Summer Vacation was almost over and it was hot. Sans decides to use his shortcut to take them there, but only for 300 G or a joke that could make him laugh. Asriel and MK fail, but Frisk manages to catch him off guard by insulting him, so he agrees to take them back to the Underground first thing tomorrow as he bids them a goodnight.
The next day, Sans arrives at Toriel's house with Papyrus, where Frisk, MK, and Asriel, who has turned back into a flower temporarily since the pieces of his soul won't fuse together, are waiting for them. Sans shares a few jokes with Toriel and promises to bring them back soon as they leave.
River Person steers his boat back to Mt. Ebott. As they get off the boat, he warns Sans of not listening to the static for too long and of the man who came from the other world. As Sans questions those words, Papyrus compares them to what he said to him, the man who speaks in hands, in which he thinks is Grillby. As everyone walks up the mountain, they share dreams of what they had the last night (Asriel's being Underfell and MK's being Underswap). As they laugh over this, the positive emotions cause Asriel turn return back to his normal state, inside the bag Frisk was carrying, thus making them topple over. After helping them up, Sans uses his powers to activate the 'shortcut' and open a vortex that brings them to Snowdin.
As they arrive, Sans and Papyrus reminisce the times they had living here, until Papyrus is hit with a snowball thrown by Frisk. Sans then "attempts" to avenge his brother by throwing one back, but effortlessly tosses it and rolls to their feet. Sans then watches everyone play in the snow until warning them that Toriel's giving them a warning to come back. As they begin to walk back to the spot of the shortcut's summoning, Sans attempts to open his shortcut, but for some odd reason, he can't. So they head for the one in Waterfall. As they walk through the raining area, Frisk, MK, and Asriel decide to run up ahead, much to Papyrus's concern. Sans, however, tells his brother that they'll be fine.
However, they are nowhere to be seen behind the corner they passed. As Papyrus shouts for them, Sans stands aside, looking scared and worried. Papyrus then divides they bring in the Canine couple to sniff out their scent and track them, so he calls them. Sans then hears rustling and snoring from a bush. As he investigates it, he sees Alphys napping there. He wakes her up, and much to her shock, she doesn't know how she got there, as she was last with Undyne back at their house. When being asked on where Frisk and the others where, Sans's attention gets caught on a looming shadowy figure approaching Alphys from behind. Seemingly knowing who that was, Sans pulls Alphys aside and tells her that they should contact Toriel and Asgore, as he has a very bad feeling.
Everyone now shows up, looking for the children to no avail. Sans sits in a rainy part of the room, looking quite gloomy. He then hears his brother talking through an Echo Flower. As he was about to ask what he was doing, Papyrus shushes him, claiming he heard them through the flower. Believing it was either from tiredness or that it was they're conversation while passing, Sans was doubtful that this could help. Papyrus then holds his brother close to the flower, and he hears Asriel talking to someone else about sharing something with the humans. Knowing well that this could give them clues, Sans and Papyrus await next to the flower.
A while later, the two have yet to hear anything new. As Sans began to drift off, he was awoken by Papyrus, who heard more talking through the flower. In fact, it was Asriel and MK talking to them. They begin to converse with one another on their whereabouts. They explained that they walked through a door around the corner and through a mirror and then ended up in another world where monsters chose to live in the mountain instead of being sealed within it and are still at war with humans. There were also other versions of everyone and that the humans have taken Frisk to their village, where the Sans from there says it would be too dangerous to get them on the Humans' territory. They also mention that monsters bleed in this world, even those who aren't from it, as it happen to MK when he was wounded by the humans. Sans devises they stay with the other versions of himself and Papyrus and form a plan while they go to investigate more of the corner where they disappeared.
Sans eventually arrives back in the True Lab (presumably by shortcut) and uncovers a hidden doorway, which leads to his old office. He proceeds to uncover a broken portal device and comes to conclusion that what he saw wasn't a dream.
It then flashes back a few years ago to when Sans was still working for Gaster and when Papyrus was still a toddler. As he receives a text that Asgore that he and the others would be late. As Sans begins to sleep again, he hears Papyrus' voice from inside the portal, which was functioning back then. Worried for his brothers safety, Sans attaches himself to a wire and the other end to a machine and jumps inside. He soon arrives in another part of the mountain and finds Papyrus. As he converses with "his" brother, a voice his heard and another Sans shows up. This Sans forces Papyrus to be by his side and the original is awestruck by these events. Suddenly, Gaster notices Sans in the portal and he and Asgore pull him back to the other side. Shortly afterwards, the device blew up and the two skeletons shield themselves. However, Sans is cut by some of the debris. As everyone chastises Sans for his motives, they all, including Sans, become concerned when they see him rapidly bleeding from his cuts and his soul is a light blue color.
Back to the present, Sans is trying to process the events when the door behind him closes and three hands with holes in the center pin him to the wall. "Alphys" then reveals herself and Sans recognizes as this not being her. They confirm this to be true as her face begins to shift into someone familiar. He then shares his backstory, who he was and why he doesn't exist, only for Sans to shut him down by saying he doesn't know who he was. After faling to convince him to help carry on his plans with Frisk, Asriel and MK, Gaster attempts to kill him.
Sans is a calm, laid back skeleton who enjoys taking things easy and cracking jokes and puns whenever the chance comes. He is also shown to be very smart from his past as a mentor of the original Royals Scientist, given his studies of 'the other world', and some other stuff about Determination. However, he can be quite scared of his own past, as when he saw the face in his folders, he remembered something horrible that seemed to haunt him, despite not knowing what it is. He is also shown to be loving towards his friends and family, and can be worried if something bad happens to them. Such as when Frisk, MK, and Asriel went missing, he was very worried and may have suspected what went wrong. He is later relieved when he founds out they're okay, but was surprised when learning that they are in an alternate reality.
Powers and Abilities
Sans has the abilities of his game counterpart. That being said, the Gaster Blasters, Blue Magic, Telekinesis, and Karma. He is shown to have been able to summon Bones. He hasn't used these powers to fight Frisk, as in their description, they have never done the Genocide Run, so there was no reason to harm them. He is also capable of using his shortcuts in specific places, presumably only in the Underground.
Papyrus: Sans loves his younger brother very much, but that does not stop him from annoying him with his puns and jokes. He is also supportive of whatever his brother does, mainly puzzles and japes. They are shown to work well as a team, given that they agree of most things that seem peculiar to them.
Toriel: Sans and Toriel would crack jokes with one another throughout the doors of the Ruins. They were both quite excited when they met face to face. After arriving on the surface, they are still quite close with one another. However, Toriel may feel Sans's laziness could impact how responsible he is, as when they were told to return home from Snowdin, MK then asks if Sans could ask Toriel for some more time, as she might say yes to him. Sans then denies this.
Alphys: Sans first met Alphys when she asked to speak with him on his past. When she began to brake down from her lack of social skills, Sans made her feel better with a joke, allowing her to speak more confident to him. She was horrified when Sans learned of the amalgamates, expecting him to hate her. Sans, however, did not, and rather consoled her and kept it a secret.
After their meeting, Sans and Alphys continued to hang out outside of time, as confirmed by Undyne, who sees Sans as a bad influence on her. Alphys has begun sleeping a lot more like Sans, and even acted more relaxed. They may hang out a lot more than expected as well, because Alphys knows of the face Sans makes when he is scared or serious, which she considers creepy. This also lets her know that something may me wrong, as Sans is normally relaxed, even in dreadful situations. Sans also does not wish to harm Alphys, as he prevented his bones from causing too much attack damage when she was possessed by Gaster. However, he was forced to attack her with a bunch of Gaster Blasters when he was nearly killed by a giant Dragon Blaster.