Sans

Sans, despite suffering from Major Depressive Disorder (MDD), has managed to evade being put into UMH. He regularly visits his brother Papyrus, and after returning from UMH on one occasion asks Frisk to break Papyrus out and bring him home.

Appearance
Sans wears the usual blue hoodie and pink slippers. However, when his depression hits him hard he opts to wear an oversized red hoodie and navy blue slippers because they better fit his mood.

Personality
Sans' personality is mostly the same as Undertale Sans'. He still tells puns religiously and is incredibly lazy, but now he has open fits of depression. They usually start after he's fought with Gaster, when he's done too much thinking by himself, or after he has too much ketchup. Sans is often neglected; this leaves him wishing Papyrus either wasn't the way he was, or wishing he wasn't around at all.

Papyrus
Sans loves Papyrus with all of his heart and wants to be a good big brother, but also holds much resentment for him. Since Papyrus is the favored son, he gets all of the positive attention that Gaster has, which leaves Sans in the way of the bad mojo. This further ruins his feelings for Papyrus, and on some occasions he may lash out at said brother (though will always apologize immediately after).

W. D. Gaster
Sans and Gaster's relationship is not the best, even though the two try to make amends on occasions.

Lucario
Sans has some beef with Lucario and does whatever he can to keep him away from Papyrus and Blue. For whatever reason, the two butt heads and, if left alone for long enough, Sans may try to attack Lucario.