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Sans is the secondary main character of Re:Tale - Bringing Life to Another World. Gaster is canonically his father in this A.U.
The story is sometimes told from his perspective.
It's likely that there is nearly no difference between Sans' in-game appearance and his appearance in this A.U. The only one that has been mentioned is that he's slightly shorter than Frisk, who is slightly shorter than Papyrus in Re:Tale; the author made it very clear that Papyrus was not the extremely tall skeleton a lot of fanart shows him as.