"SCREW IT!! WHY SHOULD I TELL YOU THAT STORY, WHEN YOU'RE ABOUT TO DIE?! NGAAAHHHHHH!!!"
– Sans before his battle
Sans is passionate about everything he does, acts quickly and is steadfast on his beliefs. Though he wants to defeat the protagonist, he tries to play fair and explain how blue mode works. Alphys taught him the values of pacifism, which is why he states the protagonist is "a wimpy loser with a big heart". When first encountered, he wants to take the protagonists soul and break the barrier, but if he is shown mercy, he's quick to defend the protagonist from Alphys. He loves to help others, and mentors Scora and Catty. He is also sarcastic and cynical. He likes to watch anime with his brother, and was told it's human history, so he regards human history as exciting and cool. He has a lot of Determination, and when he's dying, he begins to melt, as he has lost sync with his Determination.
During his battle and the pursuits through Waterfall, he wears a suit of armour, that is shiny and silver. Prior to his battle, along with the armour, he wears a helmet, that is also shiny and silver. After his battle and during his hangout, he wears a black T-shirt, light jeans and blue boots. During the Genocide battle, his armour is similar to Undyne the Undying's, but instead of a spear, it's a bone coming through his right eye.