Sans AU Headcannons

Blue

-The reason why Blue sometimes has murderous tendencies is because of the resets. Basically, anyone that looks like Chara, or is holding a knife in a very suggestive way will trigger it. Sci created a chemical that makes Blue's eyes turn red so that they know when he changes.

-In my world, Blue isn't a yandere. His brother had told him not to fight the human. After a while though, he checked, and saw his brother dying to the hand of the human. Because of this, the code that stopped him from remembering the resets broke and he developed a strong hatred for Chara. He ended up killing Chara before forcing them to reset the world.

-Blueberror is a good friend to them all, as strange as he might be. Ink was a little pissed because of the way he was treated, but those feeling died down after a while. Blueberror is an outcode separate from Blue and he lives in an empty genocide timeline, where everyone including Chara died.

-Blue is great at encouraging. Look at him, you can't possibly genuinely refuse his request in front of him.

-Blue is way better at fighting than most people think because he both has the damage and health of a Papyrus but the awareness and judgement of a Sans.

-Blue cooks well, actually. He likes cooking with Horror, slowly helping him to stop his cannibalistic and human-eating habits.

-Blue makes a good therapist. He's great at listening and encouraging you to do better and finding better ways to your problem. Dream always goes to him for advice.

-Blue has...a conflicting opinion on Dust. He understands why Dust did so, but he doesn't really approve of Dust continuing his murder after his AU was dead. He helps with that too.

-Blue and Ink (and sometimes Sci) are the therapists of the sanses. Then Dream is Blue's therapist and Error is Ink's therapist-

-Blue also has a conflicting opinion on Ink due to his vials and all, but that opinion along with Dust's faded with time, especially when he saw Error with Ink. He realized that while Ink's emotions weren't entirely real physically, he could still choose which ones to act upon. And Dust, he realized just how insane he really was.