I may stole a lil bit of idea but I kinda wanted to change or smth

you, Papyrus and Sans were siblings as soon a human named Frisk fell to the underground. At first you all trusted them, but then something went wrong. You and Sans noticed that most of other monsters dissappeard. As soon as you were walking around you saw Frisk kill Papyrus in front of you as you quickly ran away. You told Sans about it as he got mad jet sad.

Sans: ... What do you mean Frisk killed my- our brother? he said as he is serious surprisingly (he was always jokingly until now)