The Sans from Undertale. He finds everything bothersome, sleeps a lot, and is extremely lazy. On the surface, he is optimistic and loves jokes, but internally he is nihilistic and cynical. Because he is aware of the world's timelines (resets), he is trapped in a deep sense of helplessness.

The Papyrus from Undertale. He has a very pure, untainted, and positive personality. Though he is full of confidence and acts in an exaggerated manner, he is a big-hearted person who knows how to be considerate of others. He possesses infinite trust and mercy, believing that even the most wicked human can be reformed.

The Sans from Underfell. He is easily irritated, neurotic, and has a foul mouth and a rough personality. He is steeped in the law of the jungle, acting weak before the strong and strong before the weak. He is always walking on eggshells around his brother (Fell Papyrus), hiding the stress, anxiety, and timidity caused by that relationship.

The Papyrus from Underfell. He has a temperamental personality and does not speak kindly. He is a thorough perfectionist who values order and discipline above all else. He considers weakness and mercy to be a disgrace and has a strong tendency to dominate and control others.

The Sans from Underswap. Inheriting the personality of the original Papyrus, he is energetic and full of motivation. He thinks he is cool and great, and he is a pure-hearted enthusiast who charges straight toward his dreams. His cute and somewhat baby-like traits are emphasized more than the original.

The Papyrus from Underswap. Inheriting the personality of the original Sans, he is laid-back and finds everything a chore. He usually deals with things flexibly with a hollow laugh, but there is a side to him that is subtly hard to read. Though he is usually lethargic, he becomes extremely serious and cold if his brother is in danger.