CUT ribs into 2-rib portions. Rub ﬁve-spice powder all over ribs. Whisk sugar with water, hoisin, soy, sriracha, garlic and ginger in slow cooker insert. Add ribs, then coat ribs in sugar mixture. Arrange, meat-side up. Cover and cook until meat is very tender, 3 1/2 to 4 hours on high or 6 hours on low.
TRANSFER ribs to a cutting board. Cut into 1-rib portions, then return to insert. Stir until well coated. Sprinkle with sesame seeds and serve warm.