Sans is the brother of Papyrus and the snowdin sentry. He first appears in the snowdin forest.
He still wears the same clothing, but it's more dirty from blood. His eye always glows red. He's got big cracked hole in his head. Sometimes he's portrayed carrying a big axe, but in the original comic Sans isn't seen carrying any weapon (Expect one mini-comic, where is Sans seen carrying a bear trap), he is also very scary because he kills for fun.
Sans looks pretty much bored with everything.He seems to be perfectly fine with killing and eating humans. Sometimes, it seems like he is enjoying it. However, he is cares for his brother deeply. Like the original sans, he still sleeps on his sentry station. He also enjoys making head dogs (hot dogs made from severed heads), and cruel pranks.
Then he appeared in one panel of the mini-comic Fresh HotDogs and Everlasting love.In the third mini-comic Date with Sans he and Aliza stared at each other for 10 minutes, then Aliza flirted with him, he bursted in laughter, and then they had normal conversation.
Sans made his first appearance at the Ruins, where he killed Aliza with his bones, after Toriel gave him a signal. When Aliza became alive again, he attacked again, but Toriel protected her.
Snowdin forest Edit
Then he appeared at the forest, and scared Aliza. He lended her a hand with a spinning spike attached to it. He was gripping Aliza's hand for a while, until he finally stopped. Then he told her that Papyrus wants to capture her, and told her to hide behind a corpse. When Papyrus came, he told him where Aliza is hiding. After the second puzzle (orb and beartrap), Sans tried to tear Aliza's ear off, because he realized that she can save, and he thought of it as cheating. Then he heard some growling and ran away.
He appeared again, when he offered Aliza his Head dog. Aliza accepted Papyrus's spaghetti instead. Then Sans scared her, when he revealed, that the spaghetti is made of children that fell before Aliza.
Snowdin town Edit
We don't see him again, until scene where he teleported Aliza from Grillby's. Aliza is half-cooked, and Sans probably hasn't ate in ages, so he tried his best not to eat Aliza alive.
Aliza - Sans doesn't really care about capturing humans. But he likes hurting them for fun. His gore puns make Aliza really uncomfortable. Beyond this, Sans tried his best to resist the urge to eat half-cooked Aliza, and he also teleported her from death, so he might care.
Toriel - It seems like they are still in contact. He was the one who told her how terrible the world outside the Ruins is at the moment, which seriously damaged her sanity. He also tried to prevent Aliza from escaping the Ruins.
Undyne - Sans hates her. He calls her queen Undick, and in the game, he said:"Personally, I kinda want her dead. But then, who'd be left to rule this paradise?" It was confirmed, that she was the one who broke his skull because he wasn't following her orders.
Papyrus - Their relationship is pretty much the same. Sans convinced him to eat the humans, so he won't die from starvation.