For more about Canon Unexpected Guests, please explore it on Tumblr and Deviant-art
"You really wanna know the truth? you wanna ruin your lives too? ok. sure. why not. What else have I got to lose at this point? none of this matters anyway so I might as well. so congrats. I hope you like your prize... Because I sure don't."
– Sans losing his temper
Sans is the main protagonist of the Unexpected Guests comic series of Undertale. He was presumably born in Snowdin of the Underground with his younger Papyrus and once worked with W.D Gaster. He now currently resides on the surface with his friends after Monster-kind was freed. But Sans' past begins to come back to haunt him, and his friends are eager to know what is it that has been chewing him up inside, especially Flowey.
Sans is in the middle of sleeping through an anime of Mew Mew Kissey Cutie, which is being watched by Undyne, Frisk, and Papyrus. The sight of Mew Mew using her special attack causes Frisk to reminence Papyrus never showing them his. After the episode ends, Papyrus decides to go outside to duel Undyne in order to show Frisk his attack. Sans soon follows by teleporting.
Once outside, the fight starts. After a while, Papyrus summons his attack; A Gaster Blaster. At first it is just a skull, but then it turns into a giant skeleton dragon. Papyrus notices this and scolds his attack, while everyone else, including Sans, is shocked by this turn of events. While they were impressed, Papyrus asks if Sans could do this. While the latter denies this, everyone starts begging for him to get into action. Sans continues to shoot them down, until Undyne drags him into battle with Green Magic in order to bring out his power, much to his displeasure.
Undyne throws multiple spears at Sans, who deflects them with a bone shield. Due to his low HP, Sans tried making attempts of dodging, which fail miserably. Whenever it was his turn, Sans would only throw small bones up until the point where he uses his special attack; Nothing. Angry, Undyne launches many spears all at once. Without hesitation, Sans summons two Gaster Blasters and disintegrates them. Sans then decides to take a nap, now that Undyne had gotten what she wanted.
Later at night, Sans had a nightmare about his brawl with Undyne. Instead, he died in the end. Soon, it was something else attacking him, killing him over and over. After fighting back to no avail, Sans summons an attack just like Papyrus's, Gaster Blaster Dragon. He then wakes up, with Papyrus by his side. Sans then realizes that when summoning his attack in his dream, he did in real life; As there was his attack right beside him.
The next day, Undyne and Alphys drop by to bring Frisk back from their sleepover. Undyne is amazed by seeing Sans's attack like this, but is angry by him not revealing it sooner. Sans retaliates by telling her about his nightmare and warns her to not do that again in a deadpanned tone, much to her surprise.
After Toriel picks up Frisk, Sans an Papyrus go grocery shopping. However, Sans grows very tired as they walk; Papyrus then puts him in the shopping cart as they walk. Soon, he receives word from Undyne about their Blasters attacking her, but mainly Asgore. Using what energy he had left, Sans teleports him and Papyrus to their area. When they arrive, everyone is tired and injured in the demolished area. To get home, Papyrus has his attack carried Sans's injured attack with them as well as they fly along the clouds.
Later, Sans wakes up on his couch; He was surrounded by his friends, minus Papyrus and save for Flower. Still tired, Sans wanted to know what they wanted, only getting the response that they demanded to know why Asgore was attacked by his Gaster Blaster, as this could jeopardize their future on the surface. At first, Sans goes against telling them his past or how his magic works, but is eventually persuaded. He tells him his nightmare and how his attacks work; adding the reason why it attacked Asgore; It was just doing its job in harming those who received LOVE. He also tells everyone why he had such a jumpy nightmare was because he had only 1 HP. So instead of taking the blows, he dodges them.
While everyone is satisfied with their answers and are ready to leave Sans alone, Flowey isn't. He brings up the fact the Sans seems to break many laws of physics and reality with his magic, as this was the same house back in Snowdin. He also tells everyone that he's been watching Sans for a long time and that he knows the name of his attack; They were called Gaster Blasters and he shares that they were named after a man called W.D Gaster, the old royal scientist. No seems to recognize who that was, while Frisk shares some run ins with some other figures underground who seemed to mention them. Sans is shocked that Flowey knows that name and that pieces of Gaster still remain out there. Flowey then pins everything back on Sans by saying he isn't who everyone thinks he is, saying that he got rid of Gaster while working with him in order to steal his research. Undyne stands up for her friend, but Flowey tells the everyone about the chat Sans told Frisk at MTT Resort; That Frisk would be dead where they stand if not for that promise.
Frisk confirms that to be true, and Sans kept his word. Toriel is glad that Sans didn't go out of his way to harm them, but states that being shady does not earn her side of defense. As Sans reflects on some things, Flowey then taunts "Smiley Trashbag" by saying that none of his friends should even trust him, even Papyrus, as erasing someone from existence would surely erase the LOVE he received, which resolves in Sans growing mad. Flowey then says, "How's that for a little Karma?", which proves to be the breaking point for Sans as he hits Frisk and Flowey with a Blue Bone attack, much to the chagrin of his friends. Sans then sits down on the couch after Toriel "calms" him as Flowey again belittles him. One Toriel realizes that they've pushed him too far, Sans then lashes out from anger for everyone being so eager to learn about his past, even saying Flowey isn't any better than him since he knows what Karma is to begin with. He then states that he does know who Gaster was and was just like them.
Sans is a short and stout skeleton, despite being the older brother of Papyrus. Sans wears a jacket over a white t-shirt along with black gym shorts and slippers. He is always smiling no matter what the cause, even if he is angry. He has white pupils that disappear whenever he gets serious or mad. When ever he uses his magic, his left eye flashes between yellow and blue.
Sans has a tired and lazy persona, who barley puts effort into anything except cracking jokes and puns, talking about how cool his brother is, and fighting, which he does not enjoy. Otherwise, he tends to have a knack for being a comedian, as some would describe him. He is also very smart, which helps with stuff like mathematics, engineering, and most importantly, judging people's sins. Sans does not enjoy talking about himself or his past, as he is worried what his friends and brother will think of him, his magic, and, most notably, what happened with Dr. Gaster. He also tends to have a more serious side when pushed far enough or when he is about on an inch of his low health life. Such as when Undyne used green magic on him, he grows very worried about being hit; He then tells her in a serious tone to not do that again. Sans is also prone to snapping and breaking down. Like when Flowey began to make his friends suspicous of his nature and mentioning Karma, Sans met his breaking point and attacked him with a Blue Attack, which also caught Frisk since they were holding Flowey. Afterwards, Sans grows angry with everyone for trying so hard to pry into his life and lashes out at them.
Powers and Abilities
Sans can summon Bones, Blue ones as well, and Gaster Blasters. When focused hard enough, Sans can summon his blasters as full blown dragons. All of which have an effect called Karma that drains his opponents health based on how big their LOVE is. He also can use 'shortcuts' and is capable of using telekinesis. He can also create replicas of objects, which Flower points out, such as his sentry posts and even his old house, which he uses to avoid buying a new once on the surface. With powers like these, Sans mentions that he could even dethrone Asgore if he wanted to.
Sans loves Papyrus very much. Yet he loves making puns to annoy him. He also likes to mention every now and then that his bro is the coolest. He is also proud of Papyrus whenever he decides to make a pun or a joke.
Sans considers Frisk a good friend, as they never hurt anybody. That goes for period, as they seemed to have never done Genocide, so he didn't have to fight them. He is aware of their power of Determination and Resetting. He may also seem to be annoyed with Frisk at time, as they called him shady in order to bug him into showing his attacks.
Like Papyrus, Sans loves to annoy Undyne with the pun power. In an attempt to see what Sans is capable of, she drags him into battle without permission and holds him with Green Magic. Since he couldn't move and was at risk of dying to due low health, Sans was haunted by this and strictly told her not to do it again and that they were to never fight anymore. Undyne also vouched for Sans when Flowey made him seem like the bad guy.
They would both tell jokes through the door of the Ruins and were happy when they met face to face. They still love making jokes and puns. Toriel was alarmed knowing Sans couldn't deal at least one attack. A short time later, She grew mad at him that he could have hurt Frisk if not for their promise and didn't seem to exactly trust him when He would not share details on his backstory or attacks. This was soon overshadowed when Sans broke down and blamed her and everyone else for being so engrossed with his past and how that hurt him.
Sans may have had to deal with Flowey times before when he had control over the timeline. When everyone interrogated Sans, Flowey was set on learning more of his past, and turning his friends against him. Most likely because of getting in the way of his attempted Genocide Routes. Going as far as exposing his words to Frisk while at dinner to Toriel, and making him seem like the soul reason Gaster was gone. When he mentioned Karma, Sans snapped and attacked him, and unfortunately Frisk. Flowey saw this as his chance to "expose" Sans for who he really was, but everyone saw this as him getting pushed too far. Sans then retaliated to Flowey by saying since he knew what Karma was, that couldn't have made him and better than he was. Flowey is shown with a guilty expression after this.