Papyrus is Sans' younger brother.
Papyrus appears as a much younger counterpart from his Undertale character. He doesn't wear his "battle body", but an orange sweater and sweatpants. However, he keeps his signature scarf. He also wears red shoes instead of boots.
He also has a huge crush on the protagonist and can be seen playing whith his dolls of himself, Frisk, and Sans, who apparently was getting married to Frisk and, even after saying he wasn't invited to the wedding, said that Papyrus is his best man.