When Sadie first encounters Anubis, she doesn't know who he is, only that he's "a good-looking boy of about sixteen dressed in black robes. His complexion was pale, but he had lovely brown eyes… His black hair was long and tousled" (15.21). Perhaps a tad emo for some tastes, but we could go for that.
Too bad we can't have him. He's no teenage heartthrob; he's the ancient Egyptian god of funerals. His self-summary is: "I know every death custom in the world—how to die properly, how to prepare the body and soul for the afterlife. I live for death" (28.119). This apparently comes with the bonus super power of being able to summon and manipulate mummy-wrappings into whatever shape he wants.
Anubis was one of the few gods not locked up by the House of Life… why? He's not really sure. Maybe he's not as much of a threat as the other gods, with all their drama; or maybe funeral arrangements just need to go on throughout the world. So Anubis holds the fort until whenever Osiris might return, even though the Land of the Dead isn't really working properly without Osiris being there to rule over it.
Being stuck in an in-between state has not done anything to improve Anubis's mood. The way Thoth summarizes it is: "Perhaps Anubis will be in a good mood… It happens every thousand years or so" (25.71).
The other thing is that Set is Anubis's father. They've never really met, because Nephthys gave Anubis to Osiris to raise when he was young. Anubis says that Osiris is "the only family I had" (28.165), which must mean that a) he really misses Osiris, and b) he feels guilty for missing Osiris when his real father is Set. But Set's never really shown that he cares, has he?
Anubis does agree to help Sadie and Carter by giving them a feather of truth, however. This is partly because Sadie persuades him that it'll help restore the balance of Ma'at (or at least not make it any worse), and partly because it looks like Anubis is a little interested in Sadie. His parting words to her are: "[P]erhaps you could bring me up to speed on modern courtship rituals" (28.205).
Sounds like a hot date. Just keep the funerals out of it?