Sans, also known as "Blueberry", is the younger brother of Papyrus and a major character in a fan made Undertale AU, Underswap. His motivations are to capture a human so that he can become a member of the Royal Guard, a very prestigious job.
Underswap Sans is almost exactly like Papyrus but a smaller version, and has a dream of seeing a human. Some disadvantages are that Underswap Sans can't teleport and is much weaker than the original Sans, but he can move as quick as Undertale Papyrus. Underswap Sans is very cheerful, and much more energetic than the original Sans. (Bonequarrel is the theme for Underswap Sans, and Passive Megalovania is for the Outside-Of-Underswap Blueberry). He seems to dislike the cats but Underswap Papyrus doesn't care. Like the original Papyrus, he has a catchphrase, although instead of "Nyeh Heh Heh!" It's "Mweh Heh Heh!".
Underswap Sans also likes creating meals, often being tacos, and the taste of it is indescribable as well. He is often known as "Blueberry" by fans because most of them find him adorable, as well as the fact that most of his clothing is blue.
He also seems to have an extreme intolerance to sugar, as it will make him even more hyperactive than he already is. He also seems to spontaneously combust when he consumes caffeine.
Underswap Sans' arms are by his sides, and he appears simply straight and still, facing the player like Undertale Sans. His expression is straight and smiling, the dimples missing although the edges of his mouth are tilted up to suggest something like that. He has a blue bandana that appears to have a small hole close to the centre. Whether this is an accident or not is up to debate. He does have gloves like Undertale Papyrus in his Battle scene, but they seem to be missing in his overworld figure. He has a grey sleeveless shirt with a white T-shirt underneath, along with grey shoulder pads with baby blue outlining. He wears pants with a slightly faded blue look to them, and to top it all off, he has blue shoes that match his bandana. He does not appear to have a jacket like Undertale Sans does, although Papyrus does.
Underswap Sans is in the same position as Undertale Papyrus, although much shorter. He has a dimpled smile, similar to Undertale Sans, although his eyes are usually in the same expression as Undertale Papyrus'. He has a bandana on over a shirt that ties up behind his left shoulder, which is not seen in his overworld appearance.
When Sans first met Chara, he immediately wanted to be friends with them. He is very happy to have Chara as a friend, although disappointed because he wouldn't be able to join the Royal Guard for befriending Chara, a human.
Sans is the younger brother of Papyrus. They are very close, even though Sans likes to joke around which would often annoy Papyrus a lot. However, to Papyrus, Sans is the most important thing in the world. Papyrus is generally Sans' protector, yet heavily affected by his knowledge of the timelines, expecting to see Sans again even if both of them were to die.
Sans and Alphys are best friends. Sans wants to join the Royal Guard but Alphys secretly wouldn't since she cares about Sans and refuses to see him get hurt because he is too nice and sweet to fight in a battle. They hang out all the time. Also, Alphys is the one who is training him.
Sans starts a Temmie Fan club told by Temmie themself in the Neutral Route. It is known that Temmie doesn't like Sans but it is unknown what Sans think of Temmie.
Sans doesn't know much about Frisk, but can only suspect them in Chara if they were doing the Genocide route.