Sunday Depresso is a book about two depressed guys. It was initially gonna be a just-plain-old book about depression, but then weird stuff started happening to the characters. As a result, this book ended up being about a bunch of weird magical-realism-flavored stuff, with a healthy helping of depression on the side.
The only time you get to see the two guys is on Sundays. You get to see them being depressed because they have to go to work the next day.
The two guys are Jesus and his best friend, Chief Running Dog, who initially met in the year 33 AD, and have been reincarnated. They're now roommates, living together in modern times and being depressed about it being Sunday.