If you're going to dodge the hustlers on 16th Street, there had better be a good reward.

The relleno negro soup at Ku'u Up is that payoff.

At the three-month-old Yucatecan restaurant, the soup ($9) gets its toasty campfire flavor and ink-black color from toasted pasilla chiles, and its depth from chunks of blood sausage and silky strands of chicken. Though it needs no adornment, blistered corn tortillas, pocked with browned spots, are welcome.

Ku'u Up--which is Mayan for "annatto"--is not the only place for Yucatecan food in the Mission, and as at the other restaurants, salbutes and panuchos have an important place on the menu.

Salbutes ($2.50) are crisp tortillas topped with shredded chicken or pieces of pork, cabbage, and pickled onions and jalapeños. Panuchos ($2.50) have the addition of a smear of black beans. Both are enhanced by a drizzle of the thin, fiery house-made hot sauce, dispensed from an earthenware crock on each table.

The restaurant is light on décor, unless you count the giant flat-screen television showing soccer games. Takeout might seem like a better option, but then you'd miss out on the enthusiastic waitress, who recommends the relleno negro with hometown pride.

Ku'u Up, 2052 Mission St. (at 16th St.); 415-621-5510